First, measure alkalinity (buffering capacity, carbonate hardness or KH) and adjust to the appropriate level. For every 20 gallons of aquarium water draw 3 cups of aquarium water in a clean, separate container. Then add 1/8 tsp for every 3 cups of water and mix well. Pour into aquarium and wait 24 hours for the pH to stabilize. Adjust further if needed. It is recommended to adjust the pH down only 0.2 pH per day. If your water is hard and alkaline, larger doses may be required. CAUTION: This is a concentrated product - when in doubt, less is better. If alkalinity is too low, pH can be unstable and crash. To adjust alkalinity, use Kent Marine pH Stable. When using Reverse Osmosis water or tap water that is very soft (low total or general hardness or GH) use Kent Marine R/O Right to increase total dissolved solids (GH) to the proper value.