Aquarium Pharmaceuticals pH Down lowers pH and makes aquariums more acidic. API pH Down is fast acting, colorless, easy to use and will not cloud or color aquarium water.
 
Lowers pH for freshwater aquariums
For community aquariums, soft water and live-bearing fish
Will not cloud or color aquarium water
Colorless formula will not cloud or color aquarium water.
Contains no phosphates, a major source of algae outbreaks.

The following pH levels are recommended for freshwater tropical fish:
Egg-laying fish: 6.6 to 6.8 (slightly acidic)
Community aquarium: 7.0 (neutral)
Live bearing fish: 7.2 to 7.6 (slightly alkaline)