Automatically set and stabilize pH with API Proper pH 7.5 Aquarium Water Treatment. pH is the measure of acidic or alkaline water conditions. Water with a 7.0 pH level is considered neutral. Levels over 7.0 are considered alkaline, and levels under 7.0 are considered acidic. Different fish need different pH levels to stay healthy. For example, Goldfish, Mollies, Guppies and Barbs thrive at 7.5. Levels that are too high, or too low can cause stress, illness and death and fluctuations can harm fish. API Proper pH 7.5 Aquarium Water Treatment modifies and maintains pH for several weeks while neutralizing harmful chlorine and toxic heavy metals. It also contains soothing aloe vera and electrolytes to reduce fish stress. It's easy to use and fast dissolving, making it ideal to use during aquarium setup or water changes!