It depends, generally it is best to avoid sedimentary rock as they have a tendency to turn to 'jelly' when submerged. Sandstone might not be just 'sand' it could have some limestone mixed in.
Correct. Slate is metamorphosed siltstone/mudstone and should have very little in the way of carbonates.As far as I know, slate is also a good aquarium rock, and won't alter your water chemistry in any noticeable way.
While your assertion has some truth to it, i wouldn't say that its really a fair generalization. I'm a geologist, rocks are my thing, so I'd say that unless your tank is filled with hydrochloric acid that you're gonna be fine adding your sandstone, even if it has calcareous intergranular cement. This is only for natural sandstones though, if its manmade, all bets are off. And even if it has pure limestone (calcium carbonate), the amount that would dissolve out of the pores would barely be enough to register on any kind of hardness test kits you have. I'm still of the opinion that the limestone dislike is more stylistic than a chemical detriment.It depends, generally it is best to avoid sedimentary rock as they have a tendency to turn to 'jelly' when submerged. Sandstone might not be just 'sand' it could have some limestone mixed in.
Hey, another geo. I beg to differ with you though. I am out here on the west coast of Canada (Vancouver), and if you put a piece of limestone in our water, you'd be able to read something after a day. Since we live in a natural rainforest, our water is essentially rain water, and had very little dissolved minerals (GH and KH around 2). I put a piece of tufa (coralline) rock in my 20 gallon tank (fist sized) and within a week, my GH and KH went up 4 degrees. I use it to buffer the water since I am injecting CO2.While your assertion has some truth to it, i wouldn't say that its really a fair generalization. I'm a geologist, rocks are my thing, so I'd say that unless your tank is filled with hydrochloric acid that you're gonna be fine adding your sandstone, even if it has calcareous intergranular cement. This is only for natural sandstones though, if its manmade, all bets are off. And even if it has pure limestone (calcium carbonate), the amount that would dissolve out of the pores would barely be enough to register on any kind of hardness test kits you have. I'm still of the opinion that the limestone dislike is more stylistic than a chemical detriment.