Any kind of rock that is water soluble is not suitable.
Usually water soluble rocks are made from elements or compounds that are hydrophilic, like Ca, K, N, or Mg etc...
You can usually tell if the rock will affect the GH if it is easy to break with your hands.
Clay based rocks may or may not affect your GH depending on how much iron there is in it.
Obviously calcium and magnesium containing rocks like limestone are out of the question.
Yes you can use hydrochloric acid, it is probably one of the better ones to use since it is very acidic and will react with any bases strongly if they are there right away.
Most people don't use it because it seems to be rather hard to get a hold of - legally.
Usually water soluble rocks are made from elements or compounds that are hydrophilic, like Ca, K, N, or Mg etc...
You can usually tell if the rock will affect the GH if it is easy to break with your hands.
Clay based rocks may or may not affect your GH depending on how much iron there is in it.
Obviously calcium and magnesium containing rocks like limestone are out of the question.
Yes you can use hydrochloric acid, it is probably one of the better ones to use since it is very acidic and will react with any bases strongly if they are there right away.
Most people don't use it because it seems to be rather hard to get a hold of - legally.
