Some would argue that it's Ammonia. The FIRST product of the nitrogen cycle and the primary waste product of fish. 

Environmental Threats to Goldfish Health.

Youtube Video about Ammonia with Dr Erik Johnson

Goldfish health is impacted by far more than just the ‘way’ we care for the fish, or the parasites they may contract. Indeed, their very environment is often the greatest threat to their survival. This is especially true in new, unbalanced systems where the new load of livestock and the relative lack of beneficial bacteria negatively influence water quality. Perhaps the greatest effort in the care of Goldfish is in the management of the precarious balance of the water quality.

Perhaps the most important element of “water quality” which the hobbyist should master is the nitrogen cycle. The “nitrogen cycle” refers to a natural process, which is carried out by beneficial bacteria. The process reduces fish wastes and excretions into harmless compounds in the environment. The “cycle” reduces Ammonia into Nitrite. Then Nitrite is reduced into Nitrate. Plants then use the Nitrate. 

Ammonia represents the primary waste product of fish, which starts the cycle as its initial fuel. Ammonia is a nitrogen-based molecule, which may ionize and de-ionize depending upon the pH in which it exists. Ammonia is more toxic at a higher pH. At a lower pH the Ammonia molecule becomes the Ammonium ion and is less toxic.

Twenty five percent of fishes’ Ammonia excretion is in the vented wastes. Another 75% of the fishes’ Ammonia excretion is via osmosis through the gills. Ammonia is not actively excreted and leaves the fish because an osmotic gradient exists between the higher physiological [bloodstream] level and the water’s natural amount. The problem arises when the water contains high ammonia levels. When the water has a high Ammonia level, the Ammonia does not leave the fishes’ bloodstream and so they die of “auto-intoxication”.

Ammonia is removed naturally from the environment by a beneficial bacterium that lives on all underwater aquatic surfaces [term: Biofilm], and in the filter. This beneficial bacterium is called Nitrosomonas. Nitrosomonas pares off Ammonia’s Hydrogen ions and replaces them with Oxygen molecules, creating a Nitrite molecule.

The need for Oxygen in this reaction is illustrated in the following equation:

NH₃ + (O₂ required)—(Nitrosomonas) —à NO₂ (Nitrite) + 3H⁺

In the above equation you will notice that Hydrogen ions are liberated in the reaction. These may accumulate and depress the pH of the system. It is an illustration of how the very biological activity of the beneficial bacteria in the system can “crash” or reduce the pH.

Ammonia is a clinical threat in aquariums that are ‘new’ or have not established a colony of beneficial bacteria yet. Ammonia accumulation is a big part of the “New Tank Syndrome” and one of the leading killers of fish. Once Nitrosomonas has proliferated to adequate levels, the Ammonia levels decline and the Nitrite levels increase.

The diagnosis of Ammonia accumulations is as simple as a water test. I favor Aquarium Pharmaceuticals’ Nessler’s reagent drop-type test kit. At this writing there is a simpler pad-test, which does not require mixing of reagents.  The easiest Ammonia measurement tool.

I prefer water changes in the control of Ammonia accumulations. There is a beneficial effect for overall water quality with each water change. Fish are beenfited more by this method, and there is no adverse effect on beneficial filter bacteria with the water changes. Always be sure to dechlorinate.

In the hobby right now, perceived as a simpler method of Ammonia control, folks are using water additives in lieu of proper water quality maintenance. When Ammonia starts to rise, they apply a water additive instead of reducing Ammonia production by reducing feeding of the fish. Instead of changing water, they add toxic aldehydes to bind the Ammonia. More recently, newer and safer Ammonia binding agents are available which use Sulfide ions to bind the Ammonia and are far less toxic to fish. I am very impressed by the performance of Kent Marine’s “Ammonia Detox” however even this test gives false positive Ammonia readings after it’s application. The amazing ability of this product is that the fish perk right up, and seem to be able to ignore the Ammonia after application of the “Detox” product. A similar Sulfide molecule is used in the SeaChem® product, “Prime”.

After the application of most Ammonia blocking agents, you should use a Salicylate technology test to get an accurate reading. The Nessler’s reagent in the traditional tests tends to cross react with the bound Ammonia and the ammonia-binding agent.

The clinical presentation of fish suffering under a high Ammonia accumulation is exactly like a fish that is suffering under any other water quality deterioration, or a parasitism. Hence the need for accurate testing of this parameter so you can separate the possible causes for this ‘illness’. Ammonia is directly caustic to fish surfaces, fins, and gills. Redness in the skin, excess mucus production, depressed appetite, clamped fins and lethargy are all seen in fish living in Ammonia-rich waters.

An excellent method is to take a sponge or mat from an established tank. Wring this out in a five gallon bucket and extract as much of the green to brown ‘filth’ from it as possible. This “sponge extract” has an abundant number of nitrifying heterotrophs in it. You’d simply pour the ‘extract’ into the tank that you need “Cycled” and, within 24-36 hours, you will see tangible reduction in the Ammonia levels of the system. This method does not obviate the need for a water change or two after the application, to further improve the water quality and clarity. It would be wise to cycle an un-inhabited system this way, because when you add a sufficient quantity of the “sponge extract” initially, and for a few hours, the water becomes foul in the recipient system. If the water does not go “murky brown” you did not add enough ‘extract’ to make a difference. Of all the things you could do, short of a water change, this “sponge extract” system is my favorite.

(Video on bioseeding by Dr Erik Johnson)

Zeolites are a clay resin related to clinoptilolite, cat litter, bentonite and the water softening resins used by Culligan®. In fact, rumor has it that except for the price (Bentonite is sold by the yard or ton and Zeolites are sold by the ounce) they are one and the same.

Zeolites are put in a mesh bag and when the water flows through, the resin binds up the ammonia. This does not occur in water that has been salted to any extent, and you should be aware that the resin is rapidly exhaustible. Zeolites may be recharged a couple of times by immersion in a stiff salt solution. Twenty minutes in 3.0% (seawater) can cause Zeolites to release up to ninety percent of its bound Ammonia.

To a lesser extent, the Zeolites will release some of their Ammonia when you are salting out a ciliated protozoan. You should be alert to this if you have any Zeolite in your filter when you’re salting.

Ammonia Remedies in review

• Water changes
• Aldhehyde binders
• Sulfide binders
• Zeolites
• Suspend or abbreviate feedings
• Only a few bacterial adjuvants
• Established 'Filter Extraction" Technique (Bioseeding)