Use reverse osmosis or distilled water for water changes
Add driftwood
Add peat moss to the filter
Add almond leaves
Use CO2 injection
Increase aeration if excess CO2 is causing low pH swings
Perform partial water changes with softer water
Remove carbonate-rich rocks or substrates
Use a pH-lowering aquarium buffer
Test pH, KH, and GH regularly
Lower pH gradually to avoid stressing fish