PH, which refers to the acidity or alkalinity of the water, also plays a role in algal growth. Alkaline water makes nitrogen and phosphates more available to algae, not to mention making ammonia more toxic to fish. Tap water around here has a pH of about 7.7, which is 7 times more alkaline than neutral water. Ideally pond water should have a pH between 6.8-7.2. Adding pH reducing salts to hard water will lower pH, helping to combat algae.
Keeping a few fish, particularly koi, can keep string algae levels down. Some people even throw clumps of string algae in their
pond to feed their koi! Overstocking and overfeeding, however, will make matters worse. In an average pond add 1” of goldfish
or ½” of koi per square foot of surface area. More fish may be added if a larger filtration unit is installed. Tadpoles
and snails contribute somewhat in consuming algae and leftover fish food.