AQUARIUM & POND ANSWERS;
Freshwater, Marine, Sick Fish, Lighting, Baths

Updated 9/25/13

Index:

• Ghost Knife, Electric Eel Shock
• Ghost Knife
• Elephant Nose

Can a Black Ghost Fish Produce an Electric Shock?

QUESTION:
"Can black ghost knife fish give an electric shock?"

ANSWER:
No, but black knife fish do produce an electric current.
Black Ghost Knives have a small electrode sensor near their nose to sense and smell since they have almost no use of their eyes. Black Ghost Knife fish are nocturnal and are always found looking for food at night. The sensor emits a small electric current in the water which is not felt by any other fish and will not cause any harm.

The reason the current is not felt, is that knife fish produce volts, but few amps. Even their cousin, the electric eel is capable of large voltage output, but low amps (usually around 1 amp), which is why they are not very dangerous to humans, although they can stun smaller prey.

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Further Electric Eel Information
Here is some data on Electrophorus electricus, the electric eel.

• Maximum recorded voltage: 550 volts (at 1 amp). This was recorded for a 2 m long fish (the size of the fish is related to the size of the electrical discharge).


• Length of pulses: a few milliseconds, so it's not long enough to heat up the filament on a standard incandescent light bulb.


• These discharges are usually not used to kill, but to either stun prey or convince threatening organisms to go elsewhere.


• While powerful enough to knock a person down, it's extremely unlikely electric eels could kill a person.

Reference:
Paxton, J. R. and Eschmeyer, W. N. (Eds.). 1994. The Encyclopedia of Fishes, p. 112

For those who read this and think about all the Yahoo Answers posts and other inaccurate web articles then scratch their heads thinking, “wait, this guy is stating the opposite of what most others are stating”, well you need to deeper past all these anecdotal posts from those with little understanding of the physics of electricity that come up on a Google search.
One such comment is “the electric eel can discharge 6 times the electric charge (power) of household current”.
This is incorrect when you factor in the fact that normal household current is at 10-15 amps vs. the Electric Eel at 1 amp. For example an electric heater that uses 10 amps @ 120 volts = 1200 Watts. An electric eel at 1 amp @ 600 volts is 600 watts; as well the Electric Eel only discharges for a very short periods at this voltage (often only milliseconds).

Please see this educated web page about this subject from a professor of physics:
Electric Eel at the Aquarium

This article shows the irregularity of DC voltage as well the video in this article only show low wattage Christmas lights, not a heater or other device that would use the amount of electricity to seriously harm a human:
How Much Electricity Can an Electric Eel Produce

Ghost Knife Information

A Few Facts:

• Origin; Amazon and Paraguay Rivers


• Max size; 16- 20 inches


• Recommended Aquarium Size; 50 gallons (larger is even better)


• Temperature; 72- 80F


• Water Conditions; Prefers water near 7.0, but like all FW fish still needs electrolytes and calcium. VERY sensitive to poor water conditions.
  I recommend reading these two articles:
  *Aquarium Disease Prevention
  *Aquarium Chemistry; Why Calcium and Electrolytes are Important


• Foods; Prefers live foods (bloodworms, black worms, brine shrimp)


• Tank furnishings; Ghost Knife fish need a place to hide, a clear plastic tube provides this and allows you to still see your pet (Lee’s aquarium products makes one)


• Genus: Apteronotus


• Species: albifrons

Elephant Nose Information

*Related fish include the Elephant Nose Fish (Gnathonemus petersii) which have similar requirements and reach a size of approximately 10" (although the Elephant Nose are native from the Niger River area of West Africa not South America)

A Few Facts:

• Origin; Central Africa, the Zaire river basin, from the Niger to the Cameroons


• Max size; 10-13 inches


• Recommended Aquarium Size; 50 gallons (larger is even better)


• Temperature; 73°F to 84°F (22 to 28°C)


• Water Conditions; more "wider" water parameters with a pH range 6.0 to 7.6 and while preferring water more on the "soft" side, the Elephant nose does quite well in hard water and as Ghost Knives certain "hard" water mineral cations are still essential.
  Reference: Aquarium Chemistry; GH

Other Suggested Resources, Products

For up to date aquarium info (especially Redox and dispelling UV myths), please visit this site:
* AQUARIUM AND POND INFORMATION
Well researched and up to date aquarium and pond answers, help, and links. Based on 31+ years of professional aquarium maintenance experience.

Fish Diseases | How to Treat Sick Fish

*
Aquarium Lighting Resource
For in depth Lighting Information as it applies to aquarium keeping

*UV Sterilization; Benefits including Redox in Aquariums

For an experienced aquatics forum:
* Everything Aquatic

A few products that may aid in your keeping of Ghost Knives or Elephant Nose:

Reverse Osmosis Filter System

Fluidized Sand Aquarium Bio Filters
These aquarium bio filters out perform ALL other aquarium filters including Wet/Dry, Canister, etc for bio filtration.

UV Sterilizers
Value to Premium Ultraviolet Sterilizers Clarifiers, Parts, Replacement Lamps, etc. to maintain a healthy aquarium environment (including Redox) for your Elephant Nose/Ghost Knives

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Labels: Black Ghost, Electric Eel, Elephant Nose

By Carl Strohmeyer-PAMR 40+ years experience

QUESTION: Do Bio Wheels really work? Bio Wheel Review & Controlled Tests

Updated 6/3/19

ANSWER:

A Little Background

There is a lot of information about bio wheels and their importance in bio filtration in aquariums. In theory Bio Wheels are a great idea and admittedly I bought into this idea for years without testing the results to see if the hype was true.

In theory the wheel turns into the air where the oxygen that aerobic bacteria need to remove ammonia and nitrites is much more abundant than in water. Unfortunately oxygen is not the only requirement for nitrifying bio bacteria; you also need usable surface area. Bio wheels generally do not have as much useable surface area as other aerobic bacteria bio surfaces such as Sponge media or suspended (fluidized) sand media. You also need nutrients, and often the bacteria in bio wheels are not exposed to enough nutrients.
It is also noteworthy that a dissolved oxygen level of 5-7 ppm that a properly circulated/aerated aquarium should have, is ample oxygen for nitrifying bacteria.

Later, after many bio-wheels stalled and I was challenged by another knowledgeable person in the maintenance business to test them against other filters rather than rely on my anecdotal observations (he had performed such tests and knew the answer). I then decided to start testing these bio-wheels versus other bio filter methods.

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Tests, Further Information

In my first and more limited test (this is the test my colleague had performed), I removed the bio wheel penguin filters on comparable (60 gallon) established aquariums with comparable bio loads and fish and found no discernible ammonia spike.
YET when HOB filters that had running AAP Sponge Pre Filters attached to their intakes were removed, there were discernible ammonia spikes. What this means is that the working Bio Wheel was NOT the primary source or even an important source of bio filtration for the tanks with the bio wheels.
In other words these tanks were maintaining whatever bio filtration they had via other means such as gravel, filter cartridges, etc, while the aquariums with the Pre-Filters (& a couple with a sponge insert) had these bio filter mediums removed, the subsequent loss of bio filtration via a discernible spike in ammonia/nitrites was noted.

A resource for:
Filter Max Aquarium Pre Filters

The second test involved many more aquariums and was more extensive.
This second test consisted of 60 & 80 gallon aquariums (performed at my large client; Coaster Co of America which had over 20 aquariums).
Goldfish and Discus aquariums were utilized, all WELL established, with the same bio load and feeding regimen.
In fact the same aquariums were re-used multiple times in this second test as I would change out filters and then wait 8 weeks prior to re-testing with a different filter (this second test went on over a 9 month span).

In these, I ran some tests with Penguin Filters (as well as Emperor Filters) with Bio Wheels against Sponge Filters, Aqua Clears and Whisper Filters with the Sponge inserts in equal established tanks fed the same amount, then added large amounts of fish food and although the bio wheels did respond, the Sponge Filter showed a lowest ammonia spike of any filter tested when only one filter was present.

What is also noteworthy is I also used Tetra, Lees, Hagen Elite, and Chinese no name knock off Sponge filters in this test and NONE of these performed to the level of the patented AAP Hydro Sponge Filters. Part of the reason is the unique flow design, but more so to the patented sponges themselves that had more pores and did not clog as quickly as others.

A resource for:
Hydro Sponge Aquarium Filters by AAP

Another result emerged, and that is in these tests the aquariums that responded to the largest amounts of fish food being added, were the multi-filter tanks that included a HOB Filter (such as a Whisper, SunSun Power Filter, etc.) AND a Sponge Filter which provided a good example of how much Sponge Filtration via a simple Sponge Filter can improve aquarium bio capacity.

Reference:
*How sponge filters work and the benefits of using sponge filters in aquariums and ponds

These tests also included removal and/or replacement of cartridges in HOB Filters that had both cartridges and a secondary Bio Sponge, Grid, etc. such as the Whisper, SunSun etc. and of course the cartridge in the Marineland Penguin & Emperors.
Again, the Bio Wheel in most instances did not match these other filters EXCEPT in the case of power filters (of which there are many) that only had a cartridge; in the tests with these "cartridge only" filters the Bio wheel filter considerably out performed these rather basic power filters.

It is noteworthy that although the cartridge only filters were not as effective as the Bio Wheel Filters due to the fact that most bio colonies were removed with each change of the cartridge; HOWEVER when a Sponge Pre-Filter was added to these 'cartridge only' filters (such as a "Cheapie" Walmart filter used in this test), the HOB Filters with the Sponge Pre-Filter (an AAP Filter Max Pre-filter) again outperformed the Bio Wheel Filter (a Penguin in this test).

A resource for:
Filter Max Pre-Filters by AAP

Both these tests were not performed under the 100% scientific scrutiny (although the second was much more extensive and gave a better picture of nitrifying bacterial colonies), however they certainly gave an interesting snapshot of the effectiveness of different bio filtration types.

Reference:
The Aquarium Nitrogen Cycle; Bacterial Colonies

I might add that since these initial tests/studies several years ago, Fluidized Filters have emerged as THE superior aerobic bio filter (especially the newest models sold by AAP).

A resource for Fluidized Filters:
AAP Fluidized High Performance Bio Aquarium Filter

Tests I ran with Sponge Filters versus 2nd generation Fluidized Sand Bed Filters showed that even the Sponge Filters (the #5 Hydro Sponge versus the basic Lifeguard FB Filter) could not respond to increasingly higher "dumps" of fish food as fast as the FB Filters could.

As well a new variation on the HOB filter has also emerged that combines the Wet/Dry, Sponge and HOB filter with many of the attributes of these three before mentioned filters and that is the Internal Wet/Dry such as the ReSun BF 100 or the filter found in Bio Cube Aquariums. These are in many ways similar to a large Aqua Clear filter, except with the ability to add external devices such as a UV Sterilizer.
My reason in pointing out these filters is that there are even newer more effective alternatives to Bio Wheels currently available that are not expensive either.

This is not to say a bio wheel does not work at all, especially if there is less build up deposits on the bio wheel fiber.
What is much more important is to have an adequate amount of dissolved oxygen through agitation of the water surface, which is where oxygen and other gasses are exchanged from the atmosphere and the aquarium. I have found a porous sponge filter media to maintain more bacteria in well oxygenated water.

This is an important point as although air can contain much more oxygen necessary for aerobic nitrifying bacteria (which is the theory behind bio wheels), the fact remains that the nitrifying bacteria do quite well at the normal dissolved oxygen level of 5-7 ppm of most adequately circulated and properly stocked aquariums.
In fact a somewhat unknown filter; the Fluidized Filter will out performed bio wheels and wet/dry filters, even Sponge Filters in later tests and yet these are "sealed" filters, which further blows the argument for Bio Wheels out of the water that states the oxygen availability of the wet/dry feature of the bio-wheel is superior for bio filtration (this comparison is based on established filters over 6 months old).

Here are a few reasons behind the poor results of bio wheels:

1. Hard water buildup; although not as much a problem in soft water aquariums, this is a major problem with hard water aquariums and especially marine aquariums (where these bio wheels are a total waste of money).
   What happens is the calcium, salts and other deposits form in the pores of the bio wheel fiber, not allowing bacteria to form there. This is the main reason for the lack of effectiveness for bio wheels.
   My tests in Discus aquariums (which are soft water) showed better results for bio wheels (although not as well as sponge or other porous media).


2. Lack of surface area; a bio wheel does not have the surface of many other bio media products from sponge media to the very porous pumice and ceramic media used by Eheim and others.
   Previously mentioned deposits further degrade the surface area. This is not to say that other filter media do not develop deposits that resist bacterial colonization, however the in/out of water nature of a bio-wheel lends itself to a much higher rate of deposits which a simply magnifying glass inspection will reveal


3. Unlike a sponge filter, especially the patented AAP/ATI Hydro Sponge Filters, the Bio Wheels have no capacity for trapping nitrogenous waste that can then be easily removed via a rinsing or similar maintenance procedure.


4. Bio wheels run in a high oxygen environment that encourages fast aerobic nitrifcation, but little else. This allows for copious amounts of nitrates to be generated in a short amount of time.
   This type of environment does not keep a stable bacterial colony to respond to sudden changes in bio load either.
   With this environment, there is also no chance for a de-nitrifying environment to establish in filters that employ bio wheels.
   It is noteworthy that these negative attributes are multiplied in the Emperor HOB Filter with spray bars running the bio wheels.


5. Bio wheel stalls; bio wheels have a bad habit of stalling or rotating too slowly for the bacteria to be bathed in nutrients. This can be only a minor reason to not have these bio wheels as this is a somewhat correctable problem. Here is a way correct this problem (this will be an on going maintenance problem).
   Make sure the Teflon ends on the bio wheel axle are clean and have no build ups of calcium you can replace these with Teflon tape in a pinch.
   Also make sure the bio wheel assembly is not to tight, simply remove the bio wheel and gently stretch the assembly apart so the wheel can spin more freely.


6. As for the Marineland Emperor Bio Wheel Filter, I have heard some unsupported arguments for this filter, HOWEVER in multiple observations where the Emperor Filter was replaced with a Hydro Sponge #5 (& smaller) (see resource earlier in the article) or another filter along with the use of SeaChem Matrix, tank conditions improved for many parameters, most notably KH, nitrates and Redox.
   
   WHY one might ask? This is where this observation can be answered with known science and that is the design of the Emperor filter lends itself to being a nitrate factory with its spray bar and irrigation of the basket area, not allowing the use of products such as SeaChem Matrix, de-Nitrate, volcanic rock, Bio Home, live rock crumbles, etc.
   
   I have also found decomposition that leads to decay of KH and reduced Redox balance with Emperor Filters.
   
   Reference:
   Importance of Aquarium Redox
   
   I will also note that I have found similar results with poor Redox, KH, nitrates with the use of wet/dry filters systems that employ bio balls and/or ceramic media (not so with Wet/Dry employing live rock and/or sponge filters).

SUMMARY;

This is NOT to say bio wheels do not work, they are certainly better than cartridge only filters! Bio wheels just do not hold up to the hype and urban myths about them in the aquarium hobby.

You can often do better with the sponge in an Aqua Clear, AAP/SunSun, AAP Tidal, or Whisper Filter, or a sponge pre filter on ANY HOB filter (AAP Filter Max), and especially a separate Sponge Filter and even more so a Fluidized Filter (which the Bio Wheel filters do not even come close to in bio capacity), even an aquarium sponge stuck inside a HOB filter without any other bio media.
I have used many Bio Wheel (Penguin, Emperor, etc.) filters over the years with good results, my point is again not that they do not work, just if you are purchasing one of these filters for the main reason of having a “better” bio filter, you are not making the best choice based on controlled test data.

HOB Filter Resources:
*AAP/SunSun Effective economy Aquarium Power Filter
*AAP/SeaChem Tidal Premium HOB Filter

I also want to be clear that if you already have a Bio Wheel equipped Penguin or Emperor that I am NOT advocating that you immediately trash this filter and run down to your local fish store (or online) to purchase a new filter, rather to consider their drawbacks and I do STRONGLY recommend the purchase of a filter such a Hydro Sponge Filter, Internal Wet/Dry Filter, or Fluidized Filter (the Fluidized filter requires a power head or canister filter to power it) to compliment your Bio Wheel equipped filter.
This is what I recommend for any filtration system anyway; the redundancy of more than one filter!

Finally, what is missed by proponents of Bio-wheels is although the oxygen aspect of the bio-wheel is one aspect of aerobic nitrification, it is not difficult to maintain adequate oxygen levels for most other aquarium bio filters in a properly set up tank.
What is more important is surface area and there are many other specific filter medias with vastly superior surface area such as nitrifying and de-nitrifying volcanic rock, Matrix, ceramic media and MUCH more.

High Surface Area Filter Media:
*Volcanic Rock
*SeaChem Matrix Aerobic and Anaerobic Bio Media
*Nirox Bio Pure Ceramic Bio Rings

Another important aspect of aerobic filtration is that the faster and more ammonia and nitrites your aquarium bio filter processes the more nitrates your aquarium will have in the end. This is especially noteworthy for marine aquariums which is why I would recommend live rock crumbles, volcanic rock, Matrix or similar filter media that has deep pores to perform de-nitrification via anaerobic bacteria and why my consideration many years back of a large bio wheel system for a marine tank was/is a bad one.
The use of a Protein Skimmer in Marine tanks can be helpful in preventing nitrate buildup as well.
Resource for Protein Skimmer: Marine Protein Skimmers

Please see this excellent article for more marine aquarium information:
“Saltwater Basics to Advanced”

More about: Aquarium Nitrates

I will also state that the design of most Marineland (Penguin, Emperor Filters) are very efficient and they are reliable mechanical filters with much less flow-by than some others, most notably Aqua Clears, so with this in mind, ANY filter decision should be based on what you need out of a filter.

For more aquarium information about aquarium filters:
How Aquarium Filters work, Different Types

Other Suggested Resources, Products, Videos

The most effective medication BAR NONE for the treatment of Columnaris in an aquarium when used as part of the four step program of Columnaris treatment.
A more synergistic combination than purchasing Kanamycin & Nitrofurazone separately.

AAP Spectrogram; Synergistic Kanamycin/Nitrofurazone

YouTube; How to: 4 Steps Columnaris Treatment Fish Bacterial Infection

This video goes over the basics of the full four step plan of properly treating Columnaris in aquarium fish and is a compliment to a FULL reading of this article.

Aquarium Lighting; Planted, Reef, more
The most complete article about the subject of determining the best lights for your reef, planted or just fish aquarium

UV Sterilization, Sterilizer Use

Aquarium Chemistry

Pond Care

NilocG Aquatics; Planted Tank Liquid Ferts
NilocG Aquatics PROFESSIONAL GRADE planted aquarium liquid fertilizer products.
Products designed for persons who want to have a more advanced planted aquarium without the hassles need for a degree in science to do so. Meant for use in "The Estimative Index of Dosing, or No Need for Test Kits" method of planted aquarium aquascaping.

AAP/SunSun HJ-1542; replaces Via Aqua 1300
This pump replaces the Via Aqua 1300 and other copies such as by AquaTop as the Premier Power Head Pump for Aquariums, Ponds, Fountains, Wet/Dry Filters. This pump is submersible with Mag drive & ceramic shaft

The best in Quartz, Under gravel, and Submersible Heaters:

Aquarium Heaters

Fish as Pets; Parasite Retailers

Celestial Pearl Danio, Galaxy Rasboras

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Labels: Aquarium Bio Wheel, Bio Wheel Review, Sponge Filter

PROPER OSMOTIC FUNCTION- ELECTROLYTES; REVERSE OSMOSIS & SOFT WATER USE IN AQUARIUM, HOW DO FISH DRINK

INDEX of this article:

• How do fish drink water
• The Importance of healthy Osmoregulation/ Osmotic Function in Fish
  this includes Freshwater, Saltwater
  & Anadromous/ Catadromous/ Amphidromous Fish


• Necessary Minerals


• MUST READ Companion Article (originally part of this article):
  Use of RO, DI, Softwater in Aquariums

By Carl Strohmeyer-PAMR 40+ years experience
Updated 10/14/18

QUESTION: "How do fish drink water?"

ANSWER:
Freshwater fish absorb most of the water they need through their skin via osmosis by producing dilute urine and actively transport essential mineral ions from the surrounding water to compensate for mineral ions lost via the urine and diffusion from the gills (osmosis is the net movement of water through a selective permeable membrane from a region of low solute potential to a region of high solute potential due to their hyperosmotic environment), NOT through their gills. The gills are for respiration.

Most saltwater fish (Hagfish, Sharks, Rays differ in osmoregulation) actually drink the water the live in, as the salt in the water is constantly pulling H2O from their bodies in a reverse respiration as their tissues are hypotonic compared to surrounding water and they must ingest large volumes of water and actively excrete mineral ions (hypo-osmotic environment).

Marine Bony fish (not Rays, Sharks Hagfish) maintain their osmotic concentration at about one quarter to one third that of sea water.
Normally in salt/sea water, bony marine fish have a tendency to lose water from their gills due to osmosis as well through their urine. Marine fish have to drink a lot of water to make up for the loss, however, as the water contains a lot of salt (35% or approximately 1.025 specific gravity) they must remove the excess salt from their system.
The sodium and chloride ions are secreted by the gills and magnesium and sulphates are excreted in urine.
An important side note is this is an active process and requires much energy which is why lowering salt levels (NOT other mineral ions) can be helpful in aiding a sick bony marine fish!

It is noteworthy that Hagfish, Sharks, Rays have similar concentrations of salts to that of marine bony fish, however, they also have very high concentrations of organic compounds which gives their internal fluids the same osmotic concentration as sea water so these fish due not generally benefit from lower salt levels when sick.

These different abilities explain why some fish such as catfish are sensitive to salt in the water, but this is also why some fresh water fish are helped by salt to generate a mucous slime coat on their skin which is necessary for disease prevention.

For proper osmoregulation electrolytes such as positive ions of calcium, magnesium and other elements are important as well.
This is important and not realized by many aquarists (especially in freshwater), however not having these electrolytes present in the water whether by depletion or by the use of water marketed as "drinking water", distilled water, or RO water that has NOT been re-mineralized can cause problems with the fish’ ability to move fluids in and out of their bodies and in the long term resist disease.

This difference also explains why when one adds commercial vitamin preparations to a freshwater aquarium, the dilution renders it 99% useless since freshwater fish absorb much more slowly than bony saltwater fish "drink". Such vitamin preparations should only be used in a food soak or similar (unless one is into wasting money by feeding the entire water column).

Another note, because most freshwater fish cannot drink their surrounding water (Salmon and others are exceptions), when you place these freshwater fish in saltwater, they actually dehydrate.

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Osmosis in fish;

Their cells must always be bathed in a solution having the same osmotic strength as their cytoplasm. This is one of the reasons why fish and other animals have kidneys. The exact amount of water and salt removed from their blood by the fish kidneys. The process of regulating the amounts of water and mineral salts in the blood is called osmoregulation. Fish which live in the sea (remember the sea is full of salt and other elements), but fish which live in freshwater have the opposite problem; they must get rid of excess water as fast as it gets into their bodies by osmosis. Osmosis is an important topic in biology because it provides the primary means by which water is transported into and out of cells.

Osmosis is also important in the treatment of many aquarium diseases in both freshwater and saltwater. A general breakdown in osmoregulation due to disease, poor water quality (especially the lack of essential mineral electrolytes such as Calcium, magnesium, and Sodium) is often responsible for the bloated condition that results from excess water accumulation in tissues. This lack of proper osmoregulation can not only result in bloating, it can cause issues with disease resistance, curvature of the spine, and the ability of the fish to stabilize itself in the water.
It is common for Fish in this condition often rapidly succumb due to loss of homeostasis (the constant internal environment), essential to carrying out metabolism and other life activities. This tends to be more common among FW fish in my experience, in part due to the lack of understanding of the role that many essential minerals play in essential life processes of fish.

Generally salts (trace elements), not just sodium chloride can affect osmosis. Magnesium can also play a major role too. Calcium can affect and just as importantly BE affected by proper osmotic function.

Sulfates have been shown effective in improving nutrient absorption and toxin elimination.
Magnesium plays a role in the activity of more than 325 enzymes and aids in the proper assimilation of Calcium.

Often many aquarists understand how salt (sodium chloride) affects osmoregulation and the popular question of “Do fish drink?” however this is a dangerous over simplification as although sodium chloride (as often represented as sodium and chloride) are important, the lack of OTHER ESSENTIAL ELEMENTS including Calcium in fish can lose/leak substantial quantities of other minerals/salts into the water.

Here is an over simplification I read recently that is not necessarily wrong, but in misleading in that it implies salt is the only essential mineral:
“They (freshwater fish) absorb water through their skin and have effective ways of excreting excess liquid to maintain the salt they need”.
The implication is that the fish basically just needs to maintain salt and/or this or other minerals somehow take care of themselves.
The FACTS are that without Calcium (as tested via GH), the fish CANNOT properly osmoregulate.

For much more information about the importance of Calcium and other electrolytes, please read this article (in particular the section about Calcium):
CALCIUM, KH, AND MAGNESIUM IN AQUARIUMS; Why Calcium and Electrolytes are Important.

FRESHWATER FISH

In freshwater, a higher electrolyte level (particularly of sodium chloride, calcium and magnesium) will help pull fluids through the body which also stimulates the natural mucous coat on fish so as to resist parasites, bacteria, and fungus.
Also by pulling fluids through the body this can help with bloat, swim bladder problems, intestinal problems, and even dropsy (which I have had few problems with in clean tanks with good electrolyte/ trace element levels).

This process results in the loss of many electrolytes. Some of these trace elements can be replaced by ions contained in food but by far the most common method is through the movement of a substance against an osmotic gradient through the use of energy.
This usually involves the exchange of one substance for another. In the case of freshwater fish, Na+ (sodium) ions are taken from the water and ammonia ions are taken from the fish and they are exchanged.
This effectively rids the fish of ammonia. Chloride ions are exchanged for carbonate ions which help in maintaining the pH of the body fluids.
This is one more important reason for adequate Calcium, carbonate (KH), & electrolyte levels
Opportunistic diseases such as Columnaris, Saprolegnia (often known as fish fungus), and Aeromonas (often the cause of Septicemia are more easily prevented when osmoregulation is functioning properly in fish via adequate mineral levels.

Information on:
Columnaris, Saprolegnia
Aeromonas

However it should also be noted that before you go an dump a lot of sodium chloride (salt) in your freshwater aquarium, even for fish such as African Cichlids where this is a common practice, that overuse of salt can have negative side effects such as loss of other essential elements/minerals and general osmoregulation (& is occasionally noted as a contributing factor for the condition of Malawi Bloat).
Put another way, you want to achieve an Osmotic balance.

I prefer to use salt in fish such as African Cichlids sparingly and then bring it “up” during times of stress or suspected disease, only to bring it to low levels such as just a 1 teaspoon per 5 gallons reserving higher salt concentrations for 30 minute “salt baths” of 1-2 teaspoons per gallon when necessary for treatment/therapy.
What I (and many good research papers) find is that maintaining healthy levels of Calcium, magnesium, sodium, and Carbonates is far more important for long term osmoregulation and fish health, whether it be African Cichlids or Discus. The LACK of these other elements are often a common factor in cases of Malawi Bloat or even HITH in Discus.
See also: Hole in the Head (HITH) Disease in Fish

For much more about the correct use of salt (NaCl) in freshwater aquariums, please see this article:
“Aquarium Salt (Sodium chloride) in Freshwater Aquariums; both pro and con

SALTWATER FISH

A saltwater (marine) fish in water with a slightly higher salt level will devote more molecular energy to osmoregulation. Following this logic, if a fish is suffering from stress lowering the salt level will help the fish to recover.
Lowering the salt level (salinity) will reduce osmotic pressure within the fish allowing it to allocate more of its molecular energy to its immune system, this will help stop the stressed fish from becoming sick and can be used to treat fish that are sick.

As well, in marine fish sometimes lowering salinity to a certain point will have a reverse osmotic effect and rupture the cell wall of many parasites such as Oodinium and Cryptocaryon (this is best achieved in a 3-5 minute freshwater bath adjusted for pH).

This method of lowering the specific gravity (salt content) in saltwater to fight disease should not be taken too far.
I have heard of persons being told to keep their marine aquariums at a specific gravity of 1.012 to prevent or fight disease, however this is TOO LOW. At his specific gravity (salinity), the marine fish will not have proper osmotic function (remember, marine fish drink the water around them and at this salt level they will not get the fluids and minerals being pulled properly through their bodies which can result in water retention and MUCH worse).
The general specific gravity in marine aquariums should be around 1.019 to 1.024 for fish and around 1.022 to 1.025 for reef.
Be careful when lowering salinity as marine fish can generally only handle about 2 degrees of salt change per day (example; 1.025 to 1.023).

To treat parasite infections (such as Oodinium and Cryptocaryon), you can TEMPORARILY and slowly lower the specific gravity to as low as 1.010.
Be careful in lowering salinity with corals and anemones present as they cannot tolerate the lower salinity levels fish can.

ANADROMOUS, AMPHIDROMOUS, & CATADROMOUS FISH

These are fish that can migrate between fresh and saltwater.

• Anadromous fish live in the sea mostly, and then breed in fresh water such as the Pacific Salmon
• Catadromous fish live in fresh water and then breed in the sea such as freshwater eels of genus Anguilla
• Amphidromous fish move between fresh and salt water during some part of life cycle, although not for reasons of breeding such as Bull sharks in the Zambezi river of Africa and living in Lake Nicaragua of Central America.

Using Salmon as an example of how bony fish (other than sharks, rays, true eels) osmoregulate in these dual conditions;

Salmon spend most of their life in the open ocean, where they reach sexual maturity, but lay their eggs gravel beds at the upper reaches of freshwater streams.
When the eggs hatch, the young salmon spend several months migrating downstream to the ocean where they remain for some 3-5 years. When mature, the adult salmon return to mouth of stream where they hatched migrating upstream to its headwaters, spawn, and die.

There are osmoregulation/ physiological challenges presented by habitats as different as freshwater streams and the open ocean for which the salmon must adapt to so as to complete this cycle. The salmon uses adaptations, both behavioral and physiological, that allow it to thrive in both fresh and salt water habitats.
To offset the dehydrating effects of salt water, the salmon drinks copious amounts of saltwater.
So as an ocean-dwelling salmon drinks, it takes in a lot of NaCl, which exacerbates the salt-loading problem. However in fresh water the salmon doesn't drink at all.

Kidney function also differs between the two habitats.
In fresh water, the salmon's kidneys produce large volumes of dilute urine (to cope with all of the water that's diffusing into the salmon's body fluids), while in the ocean environment, the kidneys' urine production rates drop dramatically and the urine is as concentrated as the kidneys can make it.
The result of this is that the salmon is using relatively little water to get rid of all of the excess ions it can.

Finally, the other adaptation salmon use to deal with the NaCl fluxes driven by the gradients between the salmon and its surroundings is in their gills.
In their gill epithelial cells, salmon have a special enzyme that hydrolyzes ATP (Adenosine triphosphate).
ATP is the universal unit of energy used in all living cells and a salmon uses the released energy to actively transport both Na+ and Cl- against their concentration gradients.

In the ocean, these Na+-Cl- adenosine triphosphatase molecules 'pump' Na+ and Cl- out of the salmon's blood into the salt water flowing over the gills, thereby causing NaCl to be lost to the water and offsetting the continuous influx of NaCl.
In fresh water, these same Na+-Cl- adenosine triphosphatase molecules 'pump' Na+ and Cl- out of the water flowing over the gills and into the salmon's blood, thereby offsetting the continuous diffusion driven loss of NaCl that the salmon is subject to in fresh water habitats with their extremely low NaCl concentrations.

When a young salmon on its seaward journey first reaches the saline water at the mouth of its home stream, it remains there for a period of several days to weeks, gradually moving into saltier water as it acclimates.
During this time, it begins drinking the water it's swimming in, its kidneys start producing a concentrated, low-volume urine, and the NaCl pumps in its gills literally reverse the direction that they move NaCl (so that they're now pumping NaCl out of the blood and into the surrounding water.
Likewise, when an adult salmon is ready to spawn and reaches the mouth of its home stream, it once again remains in the brackish water zone of the stream's mouth until it is able to reverse the changes it made as a juvenile invading the ocean for the first time.

Further reference:
www.unm.edu/~toolson/salmon_osmoregulation.html

Necessary Minerals

Here are a few necessary TRACE elements/minerals (electrolytes) and their function.

• Calcium (Actually needed in more than trace amounts): Calcium helps to transport ions (electrically charged particles) across the membrane, is essential for muscle contraction, calcium assists in maintaining all cells and connective tissues in the body, and much more.
  
  With many fish, long term lack of calcium can result in the inability of the fish to properly balance and swim correctly due to poor muscle contraction ability or swim bladder issues. These symptoms can mimic diseases such as Whirling Disease when in fact there is no actual disease. Unfortunately, sometimes when a fish gets to this point, correcting Calcium and other essential mineral levels is too little, too late.
  
  Please read for more about Calcium:
  Use of RO, DI Softwater in Aquariums
  Aquarium Chemistry; Calcium
  
  For a professionally proven method to maintain calcium and essential mineral Cations in ALL freshewater fish:
  AAP Wonder Shells; Fresh, NOT Clearance Stock as sold elsewhere by discounters/Amazon


• Sodium (Actually needed in more than trace amounts which is why water from home water softeners should NOT be used): Regulates extra-cellular electrolyte, essential for the transport of nutrients across the cell membranes.


• Potassium: Regulates intracellular osmotic pressure, cell membrane potential, and salt excretion.


• Phosphorus: Energy metabolism.


• Molybdenum: Important for proper skeletal growth (very important in reef aquariums for hard coral growth).


• Manganese: Aids enzymes involved in metabolism, growth and maintenance of bone and cartilage.


• Iron: Oxygen transport in blood and muscle tissue.


• Magnesium: As stated previously, magnesium plays a role in the activity of more than 325 enzymes and aids in the proper assimilation of Calcium.


• Sulfates: Also as stated above, improve nutrient absorption and toxin elimination.


• Chromium: Important for proper utilization of sugars.


• Cobalt: Necessary for Folic Acid synthesis.


• Copper (very trace amounts): Co-enzyme for energy metabolism, aids in the protection of the myelin sheath around the nerves, important for iron absorption and utilization.

For a related post that deals with trace elements:
“Plaster in Paris in Aquariums and Ponds”

It is important to have a proper Redox Potential which describes the ability for the loss of an electron by a molecule, atom or ion to the gain of an electron by another molecule, atom or ion.
Without this reducing Redox Potential many minerals cannot be absorbed and properly assimilated. So it is very important to keep a “positively charged” aquarium or a Balanced Redox Potential via proper dissolved oxygen levels, calcium and other electrolytes, proper cleaning procedures and water changes (UV Sterilization can help too).

For more information about the Redox Potential, please see this article:
*The Redox Potential in Aquariums (& Ponds) and how it relates to proper aquatic health

For further reading on this subject, here are a few articles I recommend:

This other Aquarium Answers article is an excellent compliment:
*Tap water for my Aquarium or Pond? From Chlorine and Chloramines to Phosphates & TDS

This now deleted article is a very interesting (although somewhat dated), especially as it pertains to the benefits of lower salinity for Marine teleost/teleostei fish (ray-finned fishes):
*http://www2.hawaii.edu/~delbeek/delb11.html (now a dead link)
This point from this article is noteworthy:
"Since marine fish must constantly expel various solutes, such as sodium and chloride ions, against an osmotic gradient, a great deal of energy is required. Therefore, anything that you can do to lower the osmotic gradient will benefit the fish in terms of energy expenditure. The simplest way of doing this is to lower the salinity of the water as much as possible, particularly for a fish in distress."

*Can you say Anadromous, Catadromous, Amphidromous, Oceanodromous, or Potamodromous?

For more aquarium information, please visit this site:
* “AQUARIUM AND POND INFORMATION”

*Sodium Ions: http://www.elmhurst.edu/~chm/vchembook/142Aposion.html

Carl Strohmeyer- Copyright 2016

Other Recommended Reference & Product Sites

Aquarium Information and Resources (Pond too)


*UV Sterilization, Sterilizer Use
The above article is the most in depth and constantly researched/updated article to be found ANYWHERE on the Internet!

Fish Diseases | How to Treat Sick Fish

TMC Total Dissolved Solids Monitor

An excellent stand alone product for testing your TDS from Tap, well, or even aquarium water.
A must have for any advanced aquarium keeper.



*Ich; Lifecycle, Identification, Treatment, Prevention

AquaRay Ultra Premium Aquarium LED Lights
Highest in PUR, The ONLY LED with an IP67 rating or higher for water proofing along with a full 5 year warranty to back them up! Why purchase brands without this rating such as the Finnex, Current, or Fluval only to be essentially placing an electronic light emitting device over your humid aquarium with little or no guarantee? In the long term, you WILL PAY MORE!



*Pond Care

*Aquarium Forum; Everything Aquatic & Aquarium Forum Board

FISH AS PETS
Fish as Pets contains articles and commentary of Interest to the Aquarium Hobby

The Best in Value UV Sterilizers:
*Aquarium & Pond UV-C Sterilizers/Clarifiers

Including;

COMPACT UV STERILIZERS, Terminator 7 watt to 36 watt

*TMC PREMIUM High Dwell Time Pond/Aquarium UV Sterilizers

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Labels: Amphidromous, Anadromous, Catadromous, Do fish drink, osmoregulation, osmotic function in fish, trace minerals for fish