Water Chemistry

Water chemistry is an important part of any captured or open environment. When we talk about chemistry in an aquarium, we are including factors such as temperature, pH, and dissolved chemicals in the water. Of course, oxygenation is also key if you are keeping animals in the aquarium. At the Pritzker Marine Biology Research Center, we use some test kits for quick study, but we also use a series of probes that give us a constant record of our water quality.

A good exercise to help set up an aquarium is to explore the pH of the local water. If you are using water from the city or county, you can go to the government websites and find information about what the pH should be. You can also test the pH at your home using a variety of test kits and papers. For a simple test, you can get pH paper that is used to test swimming pools. Just run some water over the paper and compare the color that you find to the scale with the paper. If you have well water or what is referred to as ground water, your pH might be different. For small aquaria that are set up for fresh water, we recommend that you try spring water for at least part of the volume. If you are using drinking water from a government regulated source, you can find a report each year assessing that water including all of the inorganic and organic components. For instance if you go to scgov.net and search for water quality, you will see a report in both English and Spanish about our local water. Does your home water match the pH of the water at school? Does the water from your home match rain water? Test it and find out.

You can purchase test kits at a local aquarium or pet store that will help to measure other parts of water chemistry. These include things like hardness (measure of carbonates in water), ammonia, nitrite, nitrate, chlorine, alkalinity, oxygen and phosphates. You will have many different chemical cycles within your aquarium. The nitrogen cycle is among the most important regardless of whether you are setting up a fresh water or salt water aquarium.

You can purchase nitrifying bacteria at a local aquarium store or you can transfer some gravel from an already established aquarium to start your microbes in a new aquarium. Do not place gravel from a fresh water aquarium into salt water or vice versa as the bacteria will not survive. To get the cycle started, you might want to add one or two gastropods (snails) to the aquarium. These animals will produce some nitrogenous waste to help your nitrifying bacteria become established. If you are interested, create a chart when you add your snails and keep track of the ammonia, nitrite, and nitrate levels. When the levels seem to be relatively constant, if you are going to add fish, add one or two small fish to the aquarium and continue to measure these chemicals. You should see a rise in ammonia when the fish are first introduced and then the levels should start to level off and decline. The fish are producing ammonia as a waste product. As the bacteria begin to use the ammonia, you should see a rise in the nitrites. Nitrifying bacteria will begin to use the nitrites, converting them to nitrates. You MUST BE PATIENT and add animals slowly to your aquarium so that your bacteria can balance in the system. This generally takes about six to eight weeks. Be sure not to overfeed animals as you are building the system. Overfeeding will cause a build-up of waste products. You should remove uneaten food from the bottom of the aquarium.

Marine Science Outreach Initiative
New College of Florida