pH
Pure water is made up of millions of H20 molecules. These water molecules are always in motion. Sometimes, a hydrogen ion (H+) will become separated from the water molecule leaving this hydrogen ion and the hydroxyl ion (OH-) to bond with other ions. pH is a measure of free hydrogen ions. At a pH of 7, considered neutral at 600F, there is 1 free hydrogen ion out of 10,000,000 (1/107) hydrogen ions. Conversely, at this same pH there is 1 free hydroxyl ion out of 10,000,000 hydroxyl ions. Consider a pH of 8. Here there is 1/100,000,000 (1/108) free hydrogen ions and 1/1,000,000 (1/106) free hydroxyl ions. There is 10 times less hydrogen ions at pH 8 than at pH 7 and 100 times less free hydrogen ions compared to pH 6. All values above pH 7 are termed alkaline and all values below pH 7 are termed acid. Koi can live in a wide range of pH, but 7.2 to 7.8 is ideal. pH is the single most important water quality parameter. It can affect the toxicity and quantity of several of the other components of your pond water. To lower the pH of your pond you can add a water softener, try reverse osmosis, and decrease splash aeration by by-passing the waterfall. To raise pH increase splash aeration, add oyster shells, or lime.
Ammonia
75% of the total ammonia present in a pond is from one of the bi-products of fish respiration. Ammonium (NH4-), is the ionized form of ammonia. If the pH of the pond water is acid, the ammonium molecule remains intact and non toxic. If the pH of the pond water is alkaline, the ammonium molecule releases one hydrogen ion and becomes ammonia (NH3), the non ionized form. Ammonia is toxic to your fish. The amount of toxicity depends on how alkaline the water is. As pH increases above 7, the amount of ammonium transformed into ammonia is exponentially related to the pH. Water test kits measure the combined total of ammonia and ammonium. A test for ammonia should always read 0.0 PPM. (See Chlorine/Chlorimines for ammonia tests after adding a dechlorinator.) To reduce the toxic ammonia content, make a water change but be sure to add a dechlorinator, decrease feeding amount, add zeolite (never combine with salt additions), reduce fish load, add more filtration area, add a commercially prepared ammonia remover.
Nitrites/Nitrous Acid
Nitrite (NO2-) is the by-product of Nitrosomonas bacteria breaking down ammonia in alkaline water. Nitrous Acid (HNO2-) is the by-product of Nitrosomonas bacteria breaking down ammonium in acid water. These reactions are the first steps in the Nitrogen Cycle. There is again an exponential relationship with pH. As pH decreases below pH 7, the amount of nitrous acid increases and becomes more toxic. A test for these molecules should read 0.0 PPM. To reduce toxic nitrous acid, make water changes, reduce the fish load, reduce the feeding amounts or adjust the pH. Add salt at the rate of 0.2% to inhibit the intake by the fish of nitrous acid.
Nitrates/Nitric Acid
(NO3-) (HNO3) respectively are the molecular by-products of Nitrobacter Bacteria breaking down Nitrites and Nitrous Acid respectively. This is the second step in the Nitrogen Cycle. Unless found in large quantities, both are considered non toxic. To control the amount of nitrates and nitric acid, make water changes or add plants.
Water Hardness
Hard water is due to an abundant number of salts such as calcium and magnesium. Koi can cope with a wide range of hardness. There are two major benefits to having hard water in your Koi pond. First, very hard water can bind some toxic metals such as lead. Secondly, hard water reduces the workload of the koi for osmoregulatory functions. A reading of 0 to 75 PPM is considered soft, from 75 to 150 PPM is moderately hard, from 150 to 300 PPM is hard and above 300 PPM is very hard. If it is necessary to increase your hardness you can add crushed oyster shells, coral or any substance that will increase the amount of calcium.
Total Alkalinity/ Temporary Hardness
A large amount of bicarbonates in the water will result in a high Total Alkalinity reading. Also knows as 'buffers', these bicarbonates dissociate and then combine with the Hydrogen ions produced by the Nitrogen Cycle and the other acids produced by the fish and organic decomposition. When Total Alkalinity is low, or is 'used', the water will become more and more acid. Combining a low Total Alkalinity with submerged plants or algae can cause a day time alkaline pH and a night time acid pH. This 'pH shift' is stressful to your fish and can lower their resistance to disease if the situation continues. Total alkalinity should be kept above 80 PPM to avoid these potentially dangerous shifts. To increase alkalinity, add sodium bicarbonate, change the water or add a commercially prepared pH Buffer.
Temperature
Water temperature has an inverse relationship to the amount of oxygen contained in that water. The higher the water temperature, the lower the oxygen saturation level. The 'saturation level' is the maximum amount of oxygen in water at a given temperature. Water temperature also affects the metabolic rates of the fish. Fish, being cold blooded, slow their bodily functions as temperature decreases. This affects all circulatory systems. If you need to reduce the temperature of your water you can add more shade, add a misting system, bypass the waterfall during the day and utilize the waterfall only at night. To increase your water temperature, add a heater, bypass the waterfall at night and reduce the shade.
Oxygen
Oxygen is needed for the normal day to day functions of a fish and by the bacteria necessary for the breakdown of the fish's waste products in the nitrification process. Factors affecting the amount of oxygen in the water are temperature, fish load, organic load, medications, and the turn over rate. All of these factors affect oxygen inversely except the turn over rate. Minimum levels of oxygen should be 5 PPM. To increase the oxygen content, add venturis, increase the turnover rate, reduce the organic load (rid the pond of any organic matter that is sitting on the bottom). Do not add aquatic plants, they will use oxygen at night.
Carbon Dioxide
A by product of respiration by fish is the bicarbonate molecule (HCO3-). When this molecule attracts a Hydrogen ion (H+), it becomes carbonic acid (H2CO3) and drives the pH lower. Aeration causes the carbon dioxide (CO2) part of the molecule to be stripped to the air and a hydroxyl ion (OH-) remains. This by definition creates a more alkaline water. To decrease the amount of carbon dioxide, add plants or increase bubble aeration. To increase Carbon Dioxide, remove plants and decrease bubble aeration.
Chlorine & Chloramines
These chemicals are often added by water companies to make water more potable for human consumption. The toxicity of these treatments depends on the residual chlorine. Treated water will loose much of its chlorine by exposure to sun light and a time period of a few days. This is not the case for chlorimines which are much harder to break down. Adding substances such as thiosulfates to bind the residual chlorine is recommended for any major water change. If you use tap water treated by these chemicals it is recommended that the residual should not be more than .003 PPM when mixed in your pond. Tap water treated with chlorine or chloramines should be added at the sump area or as far away from the fish as possible. After adding a chloramine remover, you must use an ammonia test kit that uses a Salicylate reagent and not a Nessler reagent or the ammonia test will continue to read the presence of ammonia even though it is now bound in a non toxic form and will be removed by the filter.
Toxic Metals
Most natural waters contain chloride, sulfate, carbon, calcium, magnesium, sodium and potassium. These ions serve a vital purpose in the mineral metabolism of all animals. If these ions are found in high concentrations, their toxicity is dependent on water hardness, pH, temperature and the presence of other dissolved substances. The solubility and toxicity of zinc, lead, aluminum and copper have a direct relationship to increases of pH and water hardness. To remove heavy metals, use activated carbon filtration, amquelŽ or aqua safeŽ.
Organic Compounds
Oil and grease, organic carbons, phenolic compounds, and detergents are included in this group. Much of the pollution from these organic compounds is due to runoff entering the pond. Make water changes.
Other Toxic Gases
Hydrogen sulfide is the result of anerobic bacterial action on organic matter in the pond. Ozone is being used to disinfect water in some areas. Make water changes and clean out the mulm under the filter or in the bottom of your pond.
Pesticides & Insecticides & Herbicides
These are usually introduced into the pond by runoff, precipitation or accidental spills. Make water changes.