Rocks and thier affects to water

hhhmmmmm... it kinda looks like limestone to me. if I were you, I would put one piece into a bucket of water, and then get some white vinegar and pour like a teaspoon on another piece and see if there's a reaction. if there's no reaction, I'd rinse it off really well and check it with ammonia... if still no reaction, you'd probably be safe.. but I would still check the PH of the water after a few days with the rock in it. - probably want to pour a glass of water with nothing in it at the same time and do a PH test on the water in both the glass and the rock, just to have a... whaddotheycallit... a Control. Yeah, to have a Control.

Im not sure I understand what you mean with the vinegar? Pour the vinegar right onto the rock itself? or into the bucket of water with the rocks submerged?

If you pour vinegar onto the rock it self then the limestone will react with the vinegar meaning bad things.

another rock entirely.

It's... an acid test. to see how the rock responds to various ph unbalances... you want a chemically neutral rock, one that doesn't react.

So, you've got one rock in a bucket of water. Keep it off to the side, you're done with it for now.

Get another rock (looks like you've got several rocks there, so this should work) and do the tests on it I described. look for like... fizzing or boring a hole in the rock when the chemicals are added to it.

that's just what I would do... it should tell you if the rock is safe to be in your aquarium.

I would use a stronger acid than vinegar. Many rocks have weathered to the point where vinegar will produce no reaction.

What you should do is get a small piece of the rock in question. Break it with a hammer to expose a fresh face and test it with muriatic acid. You can find muriatic acid at any decent hardware store.

Thanks Rex, my father actually suggested that to me aswell.

I went to my local grocery store and bought a bottle of pH reducer for spas. It is sulfuric acid, to my surprise. I dripped a bit on some suspect rocks and they fizzed. So, now that 8 oz bottle resides in the garage waiting for the next suspect rocks.

If it was concentrated at all (above a few molar), I'd expect sulfuric acid to attack most any rock (or other surface) you put it on. It's a much stronger acid that hydrochloric (muriatic) acid, having twice as many H+ ions. Be careful with that stuff if it's concentrated.

All acids, including carbonic, break down any rock over time. The point of the acid test for limestones is that it releases CO2 bubbles, causing a fizz = instant indication of carbonate minerals. For best results, you should do as Rex indicated and also powder the surface if possible (use a nail or file) as some carbonates will not react even on fresh surfaces.

Keep in mind that even though a rock may not be a carbonate, it may still end up releasing Ca (and/or Mg, Na and K) and creating CO3, raising pH (slowly) over time. Especially with CO2 injection. Most igneous rocks ("granite") will be like this. This is how limestone formed in the first place. If you do regular water changes I'd presume this problem to be moot.