Are these limestones?

Dec 31, 2020
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Hello guys. I'm setting up a 50 gallon aquarium that reflect the local landscape (I live in the UAE, where there are tons of limestones and granites along the hajjar mountains, from my understanding these are mostly sedimentary rocks). I've found a few good stones here (in the pic) in my last hiking trip.

View: https://imgur.com/ZxBgkwv


In the vinegar (6% acid) test on them, there was some fizz but only minor and in corrosive areas. There is a common talk among aquarium folks that limestones leach heavy metals and alter PH/Hardness of the water. These usually come from people who aren't really geologists - I was looking for some reliable info on how likely the water (my tap water ph is 7.6-7.8, water hardness 4.0 dgH, carbonate hardness 4.0 dkH) will undergo changes? I do understand it may happen given the aqaurium water ph can fluctuate slightly but shouldn't this take a very, very long time? I would highly appreciate any expert advice on this.
 

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