TEST pH 4.5-9.5 aquarium droplet test. TEST pH 4.5-9.5 is designed for measuring the pH of fresh and salt aquarium water within the range 4.5-9.5 at intervals of 0.5 pH. The wide range of pH value helps to monitor water with extremely low or high pH values such as South American black waters or alkaline waters of Great Lakes of Africa. The pH of the water is one of the most important parameters in determining the health and survival of fish. There is an optimal pH level for every species of fish in the aquarium. It should also be borne in mind that fish will not tolerate rapid changes in pH, which may cause severe damage to the delicate skin, gills, fins, and eyes. TEST pH 4.5-9.5 quickly and easily indicates whether the water in the aquarium is safe for the fish kept.