pH Down is a liquid pH lowering product for freshwater aquariums. pH Down lowers pH by neutralizing carbonate hardness in the water. Adjusting the pH to the proper level will improve fish health, disease resistance, coloration and breeding. While many common aquarium fish will live in water with a pH range of 6.8 to 7.5, a pH of 7.0 is ideal for a community aquarium containing a variety of freshwater fish. Live bearers like mollies and swordtails prefer a higher pH of 7.2-7.6. Acid-loving fish such as angelfish and neon tetras prefer a lower pH of 6.5 6.8. Each dose of pH Down neutralizes some of the carbonate hardness and lowers the pH. The pH may rebound up to the original pH if the carbonate hardness is high. Several consecutive treatments with pH Down may be necessary to lower pH, but if there are fish present in the aquarium, the pH should not be changed more than .2 in a 24 hour period. The number of doses required to lower the pH will depend on the carbonate hardness level and the desired pH level. An aquarium with low carbonate hardness may require one treatment with pH Down while an aquarium with a high carbonate level will require several.