Proper pH control is imperative to prevent the harmful effects of too alkaline or too acidic pond water on fish and plant life.
The pH range of 6 to 8.5 is acceptable for most pond life. The primary concern with pH is its direct relationship to the toxicity of ammonia and nitrite. Each pH interger above the neutral 7 reflects a tenfold increase in such toxicities.
Any pH value below the neutral 7 is considered acidic. Baking soda or ground limestone will raise the pH level.