pH Requirements for Freshwater Fish

Freshwater fish live in various environments, so there is no "ideal" pH for your aquarium. In most cases, it all goes back to the supplier and the pet shop where you purchased the fish. If the fish were content there, changes might cause shocks regardless of the pH in their natural habitat. The pH factor is closely connected to water hardness, both of which you may change if necessary.

  1. What is pH?

    • The pH is a measure of water acidity or alkalinity, and other substances. Neutral water has a pH value of 7.0. This pH value is in the middle of the scale. The minimum pH value is 0 and all values between 0 and 7, the so-called low pH, meaning that water has more acid than normal. The maximum value is 14, and all values between 7 and 14 (high pH) mean that water is more alkaline.

    Freshwater Fish and pH

    • Freshwater fish live in water with a pH factor from 5.0 to 9.0. The great majority, however, inhabit waters with a pH from 6.0 to 7.5. Examples of species that live in low pH (5.0) environments are fish from the Amazon River (tetras and discus). Some African cichlids inhabit high pH (9.0) waters. When buying a fish, the ideal pH would be that of the supply water. With exception of examples mentioned above, the majority of other species will be content with pH values between 6.5 and 8.0.

    Changing the pH

    • Pet shops offer many chemicals to alter pH levels. Most of them include phosphate and bicarbonate (baking soda). Phosphate is an ingredient in pH-lowering chemicals. It encourages growth of algae, which, in turn, lowers the pH value in their environment. Adding more plants to an aquarium also will help lower pH levels. To raise the pH value, add baking soda or a chemical with that ingredient. Removing some plants from the aquarium also is recommended.

    Water Hardness and pH

    • The term water hardness stands for the amount of dissolved minerals in water. Water with a low percentage of minerals is called soft water; water with a high percent of minerals is called hard water. The scale varies from very soft 0 to 4 degrees of hardness (dH) to very hard (over 20 dH). Changing the pH value of hard water is very difficult. To do so, you must lower water hardness first. Filter it through peat moss or use ion exchange resins. Boil water and leave it to cool before adding it to an aquarium. Boiling reduces water hardness as well.