Many factors can affect the water in your aquarium changes in pH can be caused by the breakdown of waste in your tank, or local tap water with low pH or low alkalinity. Maintaining the proper pH level of aquarium water is important to ensure a healthy environment. Tetra Correct pH Tablets maintain the recommended pH levels in your aquarium to help reduce stress due to harmful fluctuations. Add one Tetra Correct pH Tablet to each 10 gallons (40 liters) of aquarium water. To avoid drastic pH changes, check the pH 24 hours after treating before adding more tablets. For aquariums 40 gallons or larger, dissolve the tablets before adding to your aquarium. Treat monthly to help maintain ideal pH levels in your aquarium.