We’ll be closed for the week from 1pm AEST Monday April 15, reopening April 22. Orders placed after 1pm AEST April 15 will be sent when we reopen. Thanks for your understanding. Save 10% on all orders, applied automatically at checkout. Ends Friday.

API pH Down Liquid


7 in stock


API pH DOWN lowers pH to make freshwater aquariums more acidic for fish and plants

pH is the measure of acidic or alkaline conditions of water. A value of 7.0 corresponds to a neutral pH. pH values about 7.0 are considered alkaline, and pH values below 7.0 are considered acidic. Different fish need different pH levels to be healthy. Check the pH level using a pH Test Kit. pH DOWN is designed to lower the pH of aquarium water where testing has shown pH to be at an undesirable level. pH DOWN lowers pH and makes aquarium water more acidic. pH DOWN is fast-acting, colorless, easy to use and will not cloud or color the aquarium water. pH DOWN is phosphate-free and nitrate-free therefore will not encourage algae growth.


  1. Determine the pH of aquarium water with an API Test Kit.
  2. To lower pH, add ½ tsp. (2.5ml) for each 25 U.S. gallons of aquarium water.
  3. For larger aquariums, add 1tsp. (5ml) for each 50 U.S. gallons of aquarium water.
  4. Take another pH reading before dosing again with pH DOWN.
  5. Some fish may be more sensitive to pH adjustments greater than 0.2 in a 24 hour period, so changes of this magnitude should be done with extreme care.

TIP: Some water is high in mineral ions, such as carbonate and bicarbonate, which strongly buffers aquarium water and can resist a pH change or cause “pH rebound”. In these situations, repeated dosing may be necessary to lower pH.