Curious... Are there any rules on what type of rock you can use in a planted aquarium for hardscaping? I know that some type of rock contains mineral or metal traces that could be bad. I am thinking of using some smaller flagstone or slate pieces and just want to make sure it would be safe for plants and fish. Also, any ideas on what to use to hold this together in a structured wall piece? I have heard silicone and even read of a guy that used mortar. Any input, ideas, or sources of information would be greatly appreciated here. Thanks!

Slate is good if you don't want to make the water soft; limestone is good if you want soft water. That'll depend on what kinds of fish you are going to keep. Silicone should be perfect for holding everything together

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When in doubt, do a water change.

Hi. If you don´t want to change the water parameter, you must have carefull with stones. A good way to identify the stones does not contain minerals that can change the parameters, is pour hydrochloric acid on the stone (after washing and dry). If the stone bubbling is bad symptom, is from alkali origin, if it does not, is perfect for use in the aquarium. you can also use vinegar, but with the hydrochloric acid is more visible.

The slate is perfect, but carefull not all stones slabs are slate stone. The silicone must be special for aquariums.

Regards

Loren

Carefull with acid is very dangerous

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Or you can just put the rock in a container put some fresh water and another container with nothing just the water. So after a day or to compairing the PH between these 2 than you would know.

You can use the acid from many test kits..I think I used one from my Nitrate test kit once to confirm a bad rock.

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Ph Down is a good way to field test the rocks before you bother picking them up and cleaning them for use.

Vinegar is a good test as some others. The Ph Down is my fav due to being almost instant with results and the size is enough to fit in the hip pocket of a pair of jeans.