Interpreting Water Quality Tests

What do the different water quality tests mean on our maintenance reports?
​What do we test for and why?

Temperature - Many aspects of the pond’s ecosystem are affected by temperature. Aquatic plants time their growth based on the air and water temperatures. Algae and phytoplankton proliferate more in warmer water. The water temperature also determines which strains of beneficial bacteria we apply. 

Since fish are coldblooded and cannot regulate their own body temperature, the behavior of koi and goldfish is greatly influenced by the water temperature and their immune systems are compromised by extreme temperatures. In the summer it’s important to have some shade on the pond from trees, water lilies, or other aquatic plants. Once water temperatures drop below 50 ℉ their metabolism begins to shut down so feedings should cease. During the winter the fish will shelter at the deepest part of the pond where the temperatures are warmest.

Ammonia - Ammonia (NH3/NH4+) is the waste product from all the pond’s wildlife such as fish, frogs, birds as well as decaying organic matter. Excessive levels (2.0ppm +) of ammonia are toxic to your pond’s fish and a healthy pond should ideally have zero detectable ammonia. The nitrifying bacteria in the biological filter and gravel feed on ammonia and convert into nitrite (NO2- which is also toxic), then into nitrate (NO3-), which is then converted into nitrogen gas (N2).

If ammonia levels are above 0.5ppm it indicates either overfeeding, too many fish per gallon of pond water, decaying organic matter, or an insufficient biological filter. Ammonia levels will be higher in brand new ponds and the spring and fall as the beneficial bacteria are either just getting established or experiencing stresses.

Nitrite (NO2-) - After nitrifying bacteria convert toxic ammonia into nitrite it is still in a toxic form until it is converted into nitrate. A healthy level would be zero so anything above 0.25ppm indicates an issue with the nitrogen cycle in the pond. If levels are elevated, water changes (25% every two days) should be made until levels drop. The size of the filter or amount of fish in the pond may also need to be re-examined.

Nitrate (NO3-) - High nitrate levels indicate a buildup of fish waste and organic compounds that the beneficial bacteria in the pond aren’t keeping up with. This can contribute to algae blooms and a higher likelihood of fish disease. Levels should be below 40ppm in a healthy pond. ​

pH - The measure of Hydrogen ions making the water either acidic, neutral, or alkaline. A balanced pH is critical for the health of the pond and its inhabitants. Higher pH levels also increase the harmful effects of ammonia. A range of 6.8 to 8.6 is acceptable for fish and a wide variety of plants. Below a 6.8 pH causes stress to the fish and can be caused by overstocking, improper surface agitation leading to carbon dioxide buildup, or decomposing organic matter. Proper filtration, aeration, and maintenance will help to avoid these problems.

Phosphate (PO43-) - Phosphorus is usually the limiting factor in algae growth so it’s presence is indicative of string algae or phytoplankton blooms. Some common sources of phosphorus in ponds are fish food, leaves & tree debris, soil/mulch erosion, and even tap water. Ideally levels should be 0.0ppm and anything over 0.03ppm can contribute to algae growth. Performing regular maintenance, adding plants, and proper biological filtration are the best ways to reduce phosphate levels.

Total Dissolved Solids (TDS) - The amount of all chemical ions dissolved in the water such as salts, minerals, and nutrients. The main factor in your pond’s TDS level is the source water used to initially fill the pond. TDS levels will generally become higher throughout the season as water is lost to evaporation but the dissolved solids are left behind. 

There isn’t necessarily a good or bad level of total dissolved solids so comparing readings to the initial filling of the pond in the spring is important. If levels appear to be increasing steadily over time it may be necessary to perform a water change to limit the growth of algae. Installing a rainwater harvesting system will bring in a constant supply of fresh water and naturally keep your pond’s TDS low.

kH/Alkalinity (carbonate hardness) - A measure of the amount of carbonates (CO3) in the water, usually calcium and magnesium carbonates. Having an optimal level of kH/alkalinity is important for buffering the pond’s pH so that it doesn’t experience wild swings each day from the respiration cycles of the animals and plants. The IonGen also requires an alkalinity between 100-250ppm to effectively control string algae with copper ions.

gH (general hardness) - A measure of the overall amount of mineral content in the water such as iron, silica, borate, magnesium, and calcium. The more minerals that are dissolved, the “harder” the water becomes. Up to a certain level, harder water is better for koi fish as it makes their osmoregulation processes easier and harder water can also limit any toxic effects of heavy metals. ​

Copper - In ponds utilizing an IonGen system to control string algae it’s important to monitor the copper concentration to ensure the safety of the fish and the efficacy of the treatments. It is recommended that copper levels not exceed 0.25ppm since higher levels can be toxic to invertebrates and may cause long-term fish issues.

Dissolved Oxygen - All pond fish require at least 6ppm of dissolved oxygen in the water in order to avoid stress, immune system compromise, stunting, and low appetites. Below 3ppm and koi will quickly suffocate and die. Ideally dissolved oxygen should be above 8ppm for the health of koi and for beneficial bacteria to flourish. Bacteria take much longer to break down nutrients and waste in low oxygen environments so it’s important to supply the biological filter with highly oxygenated water from the surface like most pond’s with a skimmer do. Warm, stagnant water holds the least amount of oxygen so as long as your pond is being aerated and shaded properly oxygen levels should be adequate. 

​