Ammonia, NH3, measured in parts per million (ppm), is the first measurement to determine the “health” of the biologic converter. Ammonia should not be detectable in a pond with a “healthy” bio-converter. The ideal and normal measurement of Ammonia is zero. When ammonia is dissolved in water, it is partially ionized depending upon the pH and temperature.
The ionized ammonia is called Ammonium and is not toxic to the fish. As the pH drops and the temperature decreases, the ionization and Ammonium increases which decreases the toxicity. As a general guideline for a water temperature of 70°F., most Koi would be expected to tolerate an Ammonia level of 1 ppm if the pH was 7.0, or even as high as 10.0 if the pH was 6.0. At a pH of 8.0, just 0.1 ppm could be dangerous.
Test kits are available in two basic types. Both read the total of Ammonia and Ammonium, so without knowing the temperature and pH, the toxicity cannot be determined. Suffice it to say that the only good Ammonia reading is zero. The Nessler method type test normally uses drops with a colormetric chart. The Nessler test detects both free Ammonia/Ammonium and also that chemically bound with anti-Ammonia chemical treatments (more about these later).
The Salicylate type test is a dual step, using liquid, pill or powder also with an associated color chart. It takes longer to perform and measures only the free Ammonia/Ammonium. Since only the free Ammonia is harmful to the fish, the Nessler test can be misleading under certain conditions but provides additional information under others.
The recommended test kit should be able to detect 0-1 ppm of ammonia particularly for pond with normal pH level above 7.0. A wider range kit, 0 – 5 ppm, would also be useful, particularly for those ponds with a typical pH of under 7.0. An Ammonia test kit is considered to be a requirement for all pond keepers.
Ammonia tends to block oxygen transfer from the gills to the blood and can cause both immediate and long term gill damage. The mucous producing membranes can be destroyed, reducing both the external slime coat and damaging the internal intestinal surfaces. Fish suffering from Ammonia posioning usually appear sluggish, often at the surface as if gasping for air.
Ammonia is a gas primarily released from the fish gills as a metabolic waste from protein breakdown, with some lesser secondary sources such as bacterial action on solid wastes and urea.
Ammonia is removed by bacterial action in the bio-converter and some is directly assimilated by the algae in the pond. Nitrosonomas bacteria consume the Ammonia and produce Nitrites as a waste product. A significant portion of this bacterial action can occur on the walls of the pond as well as in the bio-converter. Ammonia readings may increase with a sudden increase in bio-converter load until the bacterial colony grows to accept the added material.
This can happen following the addition of a large number of new fish to a pond or during the spring as the water temperature increases. Fish activity can often increase faster following a temperature increase than the bacterial action does. A bio-converter that becomes partially obstructed with waste and/or develops channels through the media may operate at a reduced effectiveness that can also cause the Ammona levels to increase.
Chemical treatments to counteract Ammonia toxcity are available commercially under various trade names. These treatments, most of which are based on Formaldehyde, form a chemical bond with the Ammonia that prevents it from being harmful to the fish. They do not remove it from the pond. The bio converter does the actual removal.
Although most of these products use a dosage of 50 ml per 100 gallons to chemically bind up to 1 ppm of Ammonia, be sure and check the manufacturer’s directions before use. Note that Nessler type test kits will still show chemically bound Ammonia to be present until the bio-converter bacteria actually consume it. If a pond has a healthy bio-converter, there is not only no need to treat with Ammonia binding chemical agents, it is better not to use them at all.
When Ammonia is detected (assuming a pH of about 7.5):
Increase aeration to maximum. Add supplemental air if possible.
Stop feeding the fish if detected in an established pond, reduce amount fed by half if starting up a new bio-converter/pond.
Check an established pond bio-converter for probable clean out requirement.
For an ammonia level of 0.1 ppm, conduct a 10% water change out. For a level of 1.0 ppm, conduct a 25% change out. CAUTION: If the tap water has a higher pH than that of the pond, adding the replacement water may make the situation worse.
Chemically treat for twice the amount of Ammonia measured.
Consider transferring fish if the Ammonia level reaches 2.5 ppm.
If starting up a new bio-converter/pond, discontinue use of any UV Sterilizers, Ozone Generators, and Foam Fractionators (Protein Skimmers).
Retest in 12 to 24 hours.
Under Emergency conditions only, consider chemically lowering the pH one-half unit (but not below 6.0).
source : http://www.vcnet.com/koi_net/H2Oquality.html