Fish N Tips: Aquarium Water pH Levels

pH Test Kits

This week, I want to talk about the importance of the aquarium water pH levels. Knowing what your aquarium’s pH is and what that number means are two very important things every fish owner must know. A simple aquarium water test kit, available at most pet stores, will provide a reasonably accurate reading of the water’s pH.

Now, keep in mind that while pH is one of the most common concerns and it’s extremely important to keep track of it, an aquarium with a pH level that’s too high or low is not necessarily a death sentence for your fish. Some fish can survive in water with wither high or low pH, but most fish have pH requirements. Though some exotic fish are more particular about the pH they require, even most of these fish are only particular about pH when they are breeding, so the only side effect of not maintaining an ideal pH is that the fish will not spawn. Unfortunately, there is a growing trend in the pet industry to believe that the pH in a fish tank needs to be 7.0 or very close to that, but this is not always the case - some breeds of fish prefer more basic or acidic waters.

When I first started my research into all this, like most of you probably are, I found myself asking: what is pH?

pH (potential of Hydrogen) is a measure of the acidity (softness) or alkalinity (hardness) of a liquid substance. pH is measured on a scale of 1-14 with 7 being neutral. Something with a pH lower than 7 is acidic. Something with a pH higher than 7 is basic. If the solution has an equal amount of acidic and alkaline molecules, the pH is considered neutral. Water has a natural pH of 7, but the water you are using in your tank may be different because of chemicals that are suspended or dissolved in the water. These chemicals fall into three categories: acids, bases, and buffers. Acids are chemicals that lower the pH, or make the water more acidic, bases are chemicals that raise the pH of the water, or make it more basic (or alkaline), and buffers are chemicals that can “tie up” acids or bases and keep the water’s pH level stable. Different buffers will keep the pH at different values.

Aquarium hobbyists rely heavily on pH measurements for proper fish keeping. Large bodies of water such as lakes and oceans have very little pH fluctuation, making fish intolerant of pH swings. Decaying plants, left over fish food and even fish waste all have a tendency to lower pH in an aquarium, while certain types of rocks and shells can continuously release trace amounts of calcium, boosting alkalinity. Fish keeping becomes a pH balancing act, as fishes subjected to pH swings are prone to disease and early death.

Due to chemical water treatment and other factors, tap water in many large cities throughout the U.S. tends to be alkaline with a pH close to 8.0. Though drinking tap water with a high (alkaline) pH is not harmful, the declining quality of tap water over the years has resulted in many people opting for faucet or pitcher filters to remove chlorine, chloramines, pesticides, and other substances. However. these filters do not alter pH. Alternatively, many people choose to buy purified bottled water or fresh spring water, more likely to have a pH closer to neutral.

As previously stated, not all fish prefer a neutral pH level. For example, many fish that originate from South America prefer softer, more acidic water, whereas fish from East Africa do best in hard, alkaline water. Unless you intend to breed a species that is very particular about water chemistry, you may find that the stability of the pH in an aquarium (also known as kH) is more important than the exact value.

Large, rapid changes in pH are often harmful to fish. Any change greater than 0.2 in a 24-hour period will cause physical stress for most fish, too much of which may kill it.