How Do I Fix an Aquarium With Acidic Water High in Nitrites?

Nitrite and a dropping pH require your immediate attention. The same issues promote these problems with water chemistry: the biological processes that produce nitrites also lower the pH of aquarium water as a peripheral effect. On the plus side, most of the ways you can fix the nitrite issues will also correct pH.

  1. The Nitrogen Cycle

    • Nitrate is produced by the nitrogen cycle, sometimes called the ammonia cycle in aquariums. In the ammonia cycle, fish secrete ammonia. Ammonia burns tissue and is toxic. However, bacteria in the aquarium break it down into nitrite, which is still toxic, but less so. A second suite of bacteria then convert nitrite into relatively harmless nitrate and other safer compounds. However, the breakdown of ammonia and nitrite produce various acids, which lower the pH of aquarium water. This means you'll almost always see a drop in pH when you see ammonia or nitrite. Nitrite and ammonia are both toxic to fish, and a low pH is dangerous for species that have adapted to water with a higher pH.

    Addressing Ammonia and Nitrite

    • If you see elevated levels of ammonia or nitrite, you need to take a few immediate steps. First, stop feeding the fish for several days. Less foods means less fish waste. Fish can deal with a few skipped meals more easily than ammonia and nitrite. You also need to make sure you do not overstock the aquarium or add too many fish too quickly. Only add one or two fish at a time, and do not add more until ammonia and nitrite both reach 0ppm. Also, avoid overfeeding. Only feed fish what they can eat in less than 30 seconds. Lastly, remove dead fish, plants and leftover food immediately, since their rotting can produce ammonia and nitrite.

    Increasing pH

    • You may also need to fix the pH. Keep in mind that ammonia and nitrite are more toxic in water with a higher pH, so you must address any issue with these compounds first. If you have fish that prefer water with a high pH, you can buffer the pH passively with decorations that slowly release calcium and bicarbonates into the water. This includes limestone, tufa rock and coral sand. You can also up the pH by dissolving baking soda into the water. First, collect some aquarium water in a second container, and dissolve several tablespoons of baking soda in it. Then, add a few drops, wait an hour and test the pH. If the pH has gone up by .2 pH units, stop for the day and repeat the next day. Fish react poorly to sudden changes in pH, even changes towards optimal conditions.

    Water Changes and Water Testing

    • Water changes tend to address both issues. In most of the U.S. and Europe, tap water is alkaline or basic. This means it has a higher pH, the opposite of acid. So performing a water change both dilutes the nitrite and raises the pH. You should change 10 to 25 percent of your aquarium's water biweekly for freshwater tanks, and 10 percent monthly for saltwater aquariums. Test the water every two weeks in new tanks, or monthly once the tank is fully stocked. You should also test whenever you see problems, like dying fish or fish behaving unusually. Perform a water change if there's detectable levels of ammonia or nitrite.