The most common ways to test your pond water quality is with a liquid test kit or test strips:

Both of these test have the same results; however, the liquid testing kit tends to be more reliable. Water tests normally consist of a test for ammonia, nitrites, pH, and phosphates. Here are what each test will tell you about your pond water. One important point to make is that most fish health problems stem from poor water quality. Fish love fresh water and regular water changes, something like 20% every 2 weeks, will keep your fish happy and reduce the risk of poor water quality. The only way to know if your water is poor is to test for the presence of toxins in the water the most harmful being Ammonia.


Ammonia is a toxic chemical which comes from fish’s waste, which is released into the water through the gills. Ammonia can also originate from the dead and decaying plant material in the pond or from uneaten food, which is left in the water. Ammonia in the water can disrupt a fish’s ability to regulate water; therefore, hindering the ability of the gills to absorb oxygen from the water. This is the number one fish killer. In order to solve an ammonia problem, one should:

1. Do a 20% water change immediately
2. Add beneficial bacteria (a bacteria that lives in the filters and all the surface area of a pond process) to break down ammonia into less toxic nitrite
3. Temporarily “bind” ammonia with a product like ammolock and allow the bacteria to colonize to further process ammonia

Nitrites and Nitrates

As ammonia breaks down it breaks into nitrates and nitrites; nitrates are a good source of nutrients for pond plants and algae although it isn’t necessarily harmful to fresh water fish; therefore nitrates are not something a pond owner needs to test for. However nitrites can be toxic to your fish in large amounts, nitrites can cause skin irritation which is shown by rubbing and jumping, and also has a rather sinister effect on the pond fish’s blood, as it will bind very tightly with the red pigment and thereby preventing the blood cells from absorbing vital oxygen from the water. Once the nitrite has become associated with the red pigment, it turns the blood a dull brown color and hence the popular name for nitrite poisoning is “brown blood disease”. To fix a nitrite problem, regular water changes are required to reduce the concentration of this pollutant as well as beneficial bacteria to further break down the toxin into harmless Nitrate.


Another problem many pond owners have, without even knowing it, is the imbalance of the pH in the water. In Colorado the natural pH of water is around an 8. However, the pH is in all respects a measure of acidity and alkalinity, pH 0 – 6.99 is acid; pH 7.0 is regarded as neutral and pH 7.01 – 14.0 is alkaline. On the whole the pH is not generally a problem but it can have a profound effect on the toxicity of ammonia. Alkaline water, that is with a pH of over 7.01 in combination with increasing temperatures causes more of the ammonia to exist in the free form, which is very poisonous to fish. If the water is alkaline it is worth bearing in mind that this will affect the toxicity of ammonia and that even very low readings could therefore be quite serious for the welfare of the pond fish. The pH of the pond is largely dependent on the pH of the make-up water in the surrounding area and therefore it is not possible to try to control this parameter artificially. Also adding too many beneficial bacteria at one time can cause a pH drop, baking soda in small amounts can cause the pH to rise again, or there are products such as “pH down” and ‘pH decrease” to neutralize the pH.


The last toxin to test for with water tests is phosphates, and this toxin is usually only present in well established ponds. Phosphates come from broken down plant materials, tap water (some water treatment facilities put phosphates in the water to prevent pipe corrosion and reduce concentration of heavy metals) and uneaten fish food. Phosphates in the water slow the fish’s ability to take in oxygen. Products to neutralize the phosphates such as “phos-out” or “eco-fix” should be used slowly in order to get rid of the phosphate problem and not shock the fish. (Phosphates are basically equivalent to a person standing in a really smoky room; when that person leaves the room and gets purer oxygen, they cough and kind of stutter to breathe: well the same thing happens with fish but their gills can’t handle the sudden change as well.) A 25%-30% water change may be beneficial.

Contact us or stop by the Garden Center and we’ll help with any of your fish health needs!

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