Aquatic pH Testing Kit. The "pH" of the water determines the acidic or alkaline properties of your pond. Fish do best in neutral water, that is, neither too acidic nor too alkaline. Excessively high or low pH may be directly responsible for death from secondary causes (i.e. parasitic infections). Extreme pH changes will irritate the skin and gills of the fish. Formulated after Mr. O'Brien's, secretary of William Tricker, Inc.® and inventor original pH test kit.