Pond guardian tonic salt. Pond guardian assists the pond owner in safeguarding against fish disease. Pond guardian’s unique formulation helps to create the perfect environment for pond fish. This product stabilises pond water conditions, including the all important pH value. Pond guardian is a major ally in your fishes’ struggle to maintain a constant internal body environment, and helps to reduce the toxic effects of fish waste products such as nitrite. Pond guardian is one of the pond keeper’s most verdstile water treatments. 1 bag will treat a 2,273 litre pond.