How to lower Ph levels?

[titanic]

btw i couldn't take the driftwood home

 

[titanic]

I currently hold in my thank 1 male Dwarf Gourami with 2 females Dwarf Gouramis with 4 mid-size Vallisnerias, 1 Amazon Sword and a little bit of Anacharis i picked up in the lake today (Here in Panama we literally take almost all aquarium plants from lakes)

 

[titanic]

I add just a pinch of salt because it doesn't hurt the fish and prevents some diseases Why? Is it bad?