What is pH? pH is the measure of pond water acidity. A neutral pH reading is 7.0. A pH higher than 7.0 is alkaline, lower than 7.0 is acidic. Acid rain, mineral leaching, soil runoff decomposing plant and fish waste can cause unacceptable pH levels. Even tap water used to fill fish ponds and garden ponds can cause extreme pH levels. Avoid pH levels below 6.8, which will stress pond fish and suppress biological filter activity, and pH levels above 8.0, which will hamper the ability of most plants to absorb necessary nutrients.

Test pond at the same time each day for a pH reading ABOVE 8.5.
(dawn = lowest pH; evening = highest pH)
Most ponds target for 7.5pH with 100-200ppm alkalinity (normal range).
For every 0.1pH decrease needed add 1oz per 375 gallons of water.
Important: If pond contains fish and/or plants, do not drop pH level dramatically (not more than 0.5pH unit in a 24 hour period). Altering pond pH level too fast can shock aquatic life and fish.