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Pond Water Chemistry

Most people that are new to water gardening don't think about water chemistry. The best way to prevent problems is to test your pond water regularly for elements that are toxic to pond fish. These chemical imbalances in a water garden usually have no odor or visual signs until it's too late. Another great preventative measure is to follow routine pond maintenance schedules for spring, summer and autumn. A common thread in all of these is the regular addition of beneficial bacteria.

Below you'll find information regarding the causes and effects of the chemical imbalance as well as find links to products that will aid in the correction of these imbalances.

Chlorine & Chloramines

Chloramines are a combination of chlorine and ammonia, both of which are toxic to fish. As chloramines break down, either naturally or through the use of dechlorination chemicals, ammonia is freed up. This ammonia can be removed from fish ponds by using products available in the Water Quality Category. Biological filters, natural zeolites and pH control methods are also effective in reducing the toxic effects of ammonia. An activated carbon filter may be effective in removing chloramines, however, it must contain high quality granular activated carbon and must be permitted sufficient contact time with the water.

For more information about Chlorine and Chloramines, see this article.

Ammonia Buildup

Ammonia is extremely toxic and even relatively low levels pose a threat to fish health. Ammonia is produced by fish as part of normal metabolism. Additional amounts are produced from decomposing fish food, fish waste and detritus. Yet another form of introducing ammonia into a pond is doing routine pond maintenance such as the replacement of evaporated water. Tap water in many locales contain chloramines (a combination of chlorine and ammonia) to kill bacteria in drinking water.

For more information about Ammonia, see this article.

Nitrite & Nitrate Buildup

Fish waste together with uneaten food and dead fish, aquatic plants and tree debris are decomposed in a process known as the Nitrogen Cycle. This process starts by the creation of ammonia and in a nut shell, bacteria convert ammonia to nitrites and other bacteria convert nitrites to nitrates.

For more information about Nitrate and Nitrite, see this article.

Low Oxygen Levels

Low levels of dissolved oxygen in ponds are likely the most common water quality problem in fish ponds. Aeration is often necessary to prevent fish from dying during low dissolved oxygen periods. Water can hold only a limited amount of dissolved oxygen. It increases as atmospheric pressure goes up and as temperature and salinity go down. Dissolved oxygen levels of 3-5 ppm will adequately support most pond fish.

For more information about Low Oxygen Levels, see this article.

Excess Pond Foam

Surface skimmers can reduce the build up of foam. This is a swimming pool technique whereby surface water is taken directly to the filter, removing foam and the plant debris dropped in the pond that causes it. Another control technique is by the use of a protein skimmer. This technique is taken from marine fish keeping. The basic premise it to encourage the foaming under controlled conditions. This produces protein-rich foam which is collected and then removed, removing the proteins from the water that cause foam. You can also use a chemical foam remover.

For more information about Foam Buildup, see this article.

Routine Pond Maintenance

Adding beneficial bacteria periodically to a water feature is one of the most important maintenance aspects to maintain clear, healthy water. Adding these products in the spring to start the biological filtration as well as in the summer to spike the filtration periodically, and again in the fall is also recommended as a preventative measure.

String Algae

The conditions favorable to string algae are limey water with a high pH. Run off from concrete slabs, cement, soil and even lime in tap water if you top off the pond frequently can all contribute to algae blooms. Topping off the pond with tap water also feeds it nitrates and phosphates which are a food source for algae. Phosphates also come from water running off of surrounding soil. String algae can grow at much lower temperatures than most of the competing plants in the pond and so it gets a head start on all of them. For more information about string algae, check out our String Algae article.