How to make water more acidic
From The Aquarium Wiki
To make your tank water more acidic you need to add a solution which contains hydrogen ions to your water.
- These will reduce the KH (Carbonate) level in your water.
To achieve a lower pH you need to use:
These chemicals are potentially dangerous to humans and fatal to aquarium life if used incorrectly. Please consult their MSDS sheet before using.
- See also How to make water more alkaline