Fish stress causes fish disease. One of the main causes of pond fish stress is an unsuitable pH. pH is a measure of the acidity or alkalinity of the pond water. The ideal pH is between 7.0 (neutral) and pH8.0 (slightly alkaline) but pH 6.5-8.5 is acceptable. pH Adjuster for Acid Ponds will increase low pH to within the safe level to help maintain a healthy pond environment for fish, plants and other pond life.