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Hi there,

I was wondering what type/sort of rocks do not affect water hardness. What should I look for?

To test them can I use hydrochloric acid (spirits of salts we call it here) or at least my dad does

Regards darren
 

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Rocks that contain limestone will slowly dissolve in the aquarium and change the hardness level. You can use vinegar or muriatic acid to test the rocks. If it bubbles and fizzes, it will dissolve in the aquarium.
 

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Granite is always good. Most rocks with lots of holes in them are not good, with the exception of lava rocks. I don't recall a black rock that wasn't good.
 

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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.
 

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Not too hard. Swimming pool and hardware stores sell it as muriatic acid. Same thing - just be careful with it. Don't use it inside and absolutely don't spill it on your clothes.
 
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