What Are the Dangers of High or Low pH Levels?

The pH scale measures the degree that a solution is acidic (0), neutral (7), or alkaline (14). The pH scale is often used to measure water, pure water being generally a 7. In an aquarium, the optimal pH will vary according to the ecosystem you are attempting to replicate and the species you are keeping.

  1. Effects of pH on Fish

    • Exactly optimal pH is less important than maintaining a stable pH within a healthy range for your species of fish. However, when pH drops below 6, the beneficial bacteria which turns deadly ammonia into less harmful nitrites and nitrates begin to die off, causing ammonia poisoning.

    Saltwater pH

    • Saltwater fish require a consistent pH between 8.1 and 8.3. A pH which is out of range will cause stress to fish and invertebrates, resulting in poor health.

    Freshwater pH

    • Freshwater fish, depending on the habitat from which they came, live in waters with a pH ranging from 5 to 9. Fish forced to live in a pH out of their natural range may suffer from stress and illness.

    Buffering Capacity

    • The water's "buffering capacity" determines your tank's ability to maintain a pH without rapid fluctuations, which may stress or even kill your tank's inhabitants. To measure your tank's buffering capacity, purchase a test kit to measure "hardness," or concentration of calcium carbonate. Look for a reading of at least 100 mg/L. Performing routine water changes, vacuuming gravel, keeping filters clean and not overstocking your aquarium will help your tank's buffering capacity.

    Raising pH in an Aquarium

    • Using purified tap water, adding crushed coral or limestone to your substrate or filters, and creating more water flow are methods for raising pH. You may also purchase chemicals designed to raise an aquarium's pH.

    Lowering pH in an Aquarium

    • To lower the pH of an aquarium, you need to remove some of your tank's buffering capacity, or "soften" the water. Adding peat to your power filter or substrate softens water, as does using reverse osmosis or distilled water. Driftwood in a tank naturally lowers pH.