Is aquarium water testing really necessary? In a word – YES! What should be tested, and how often, is not as short an answer. In a newly set up aquarium, water testing is critical to avoid fish loss asammonia and nitrites rapidly rise. In an established tank, water testing is important to ensure the continued health of your fish.


Testing for ammonia is a must. Ammonia will be elevated during the start-up cycle in a new tank. However, ammonia can also be elevated in mature tanks if the water is not changed regularly, filters are not kept clean, if the tank is overstocked, or if medication is used that disrupts the biological cycle.


Aside from  new tank syndrome, I’ve found that pH is the most frequent cause of fish stress, which can ultimately lead to fish loss. Unfortunately, it is usually the most overlooked parameter. Fish cannot tolerate sudden changes in pH. Even a change of 0.2 can result in stress or death if it occurs suddenly.

Know the pH of your fish shop’s water , as well as your own, so you can be acclimating new fish properly. Keep in mind that if you use tap water, it has dissolved gasses as a result of being under pressure. Let the tap water sit overnight before testing the pH.


pH can, and will, change with time. Fish and plant waste, water evaporation, topping off water, and water hardness will all contribute to changes in the pH. As a rule of  thumb, pH in an established tank should be tested once a month, and any time there is a fish death or illness.

Another factor of pH is the buffering capability of your water. If your water pH changes suddenly, or drifts regularly over time, you should check the KH (Carbonate Hardness ) of the water. Consult your local fish shop for KH testing, and for buffering compounds to stabilize the pH level.


During the start-up of a new tank, nitrite levels will soar and can stress or kill fish. However, even after an aquarium is initially “cycled”, it is not unusual to go through mini-cycles from time to time. For that reason, include nitrite testing as part of your monthly testing routine. Any elevation of nitrite levels is a red flag that indicates a problem brewing in the tank. If a fish is ill, or dies, it’s wise to test for nitrite to ensure it is not contributing to the problem. The only way to reduce elevated nitrite levels quickly is via water changes.


 Although nitrates are not as toxic as ammonia or nitrites, they must be monitored to avoid stressing the fish. Nitrates can also be a source of algae problems. Nitrates will rise over time and can only be eliminated via water changes. Monthly tests are important – particularly when breeding fish, as young fish are more sensitive to nitrates than adult fish. Test monthly and keep levels low to ensure a healthy tank.


Whenever anyone complains that they cannot win the battle against algae, phosphates immediately come to mind. Phosphate serve as a nutrient for algae, and elevated levels will certainly add to your algae woes.

Although it’s rarely discussed, a leading cause of increased phosphates is dry fish food particularly overfeeding with lower quality foods that are high in phosphates. If you have algae overgrowth, test for phosphates. There are filtering materials available that remove phosphates.