Although it is possible to keep fish without knowing their pH tolerances, there are certain fish, typically more exotic breeds, that require specific pH balances in order to thrive in aquarium water. Understanding how your tank’s pH works, as well as why the different reactions that can occur, leads to a healthy aquarium with happy fish.
The pH level of the water in your aquarium is essentially determined by measuring the difference in H+ and OH- ions, knowing how these two ions regulate the acidity of the tank. Ions are a combination of two other molecules that results in a charged particle, and ions in particular are formed by the union of two other molecules, positive electrons and negatively charged neutrons. All atoms are surrounded by shells that contain electrons, the innermost one contains 2 electrons and the next shell contains 8.
The components of water, hydrogen and oxygen, are atoms that have strong reactions with each other due to their unique mathematics. Hydrogen contains 1 electron and needs one more to reach the optimal number of its inner shell – 2 – that an atom wants to have. Oxygen has 8 total electrons, but only 6 in the outer shell, which means that oxygen desperately wants to bond with other atoms to gain two electrons. Thus, oxygen reacts with two hydrogens in an ionic bond to form H2O, ordinary water. When only a single oxygen and hydrogen come together, instead of water, they form OH- which is hydroxide. Typically, the lone H+ will bind to a formed water molecule to form H3O+, which is what is measured to determine pH. The more H3O+ molecules, the lower the pH of the tank.
The pH scale runs from 1 to 14, where 1 is acidic, 7 is considered neutral, and 7+ is termed base or alkaline. The pH scale is constantly changing as new materials are introduced into the water both by human hands and by natural products from the aquarium contents. The rapid changes in pH are what is really harmful to fish because their bodies cannot cope quickly enough. Although rapid changes in pH are harmful, most fish can live in pH conditions that, while less than ideal levels, have at least stable acidity.
Ideally, you’ll want to keep the tank in the 7 to 7.5 pH range, as this is close to neutral without being too alkaline. You can adjust tank levels naturally by adding limestone to increase alkalinity and peat to increase tank acidity. Be sure to monitor your aquarium’s pH level to keep your fish healthy and happy.