Because fish originate from different bodies of water that have differing pH levels, there is not a common, or normal, pH that all fish can live in. Every fish has a different range of pH it enjoys to live in and balancing the water of your aquarium to a matching level will be very beneficial for your fish to strive. Remember that even with careful control of the aquariums pH, that the pH is not a static number. It is constantly changing due to the vast amount of influences on he tank. During the day the pH will rise, and fall later that night. PH change when fish are brought into or removed from the tank, it will change when fresher water is added, and will change depending upon the quantity of biological processes your fish go through each day.

Despite the varying levels in the tank, it is still perfectly acceptable for the tank to be within a certain range of pH that the fish of the aquarium can live comfortably in. These pH levels, which can be influenced and controlled by the owner, are important to be aware of. Each freshwater fish thrives in a separate, even if similar, range which allows you to place separate breeds of fish with similar pH tolerances in the aquarium. The following is a list of common freshwater fish and their accepted pH tolerances: Angelfish 6.5-7.0, Clown Loach, 6.0-6.5, Goldfish 7.0-7.5, Harlequin 6.0-6.5, Hachetfish 6.0-7.0, Neon Tetra 5.8-6.2, Plecostomus 5.0-7.0, Silver Dollar 6.0-7.0, Tiger Barb 6.0-6.5, and Zebra Danio 6.5-7.0. » Read more: The Importance of PH in Aquariums