List of rocks and how they affect ph/gh

[littletankbigworld]

Hello. Our LFS has a nice selection of slate and lava rock and a couple other types of rock. In my sculpture class, I have to make a sculpture using non-traditional materials and I was considering constructing something for my 29 gallon tank. However, I'm not sure how rocks like slate, granite, lava, etc. affect water parameters like ph or gh. Could anyone help me with this? I'd like to compile some sort of a useful list that myself and others could use for reference. Thanks!

 

[Doomhed]

I think slate and granite are safe bets. Don't use alabaster, as it is essentially rock-salt.

 

[emmanuelchavez]

The rocks you've listed are all safe for aquariums. If you're concerned about whether a rock will affect your water parameters, drop some vinegar on it. It'll react with the acid and fizz. Limestones are what you need to watch out for.

 

[bassbonediva]

I have black slate in some of my tanks (came as a "box of rocks" at Petco) and it hasn't affected anything as far as my water parameters go.

And thanks, emmanuel! I was trying to remember the vinegar trick, but I could remember if it was with vinegar or something else. lol

 

[emmanuelchavez]

A diluted hydrochloric acid is what I use, but not many have access to it. The only reason I have some lying around the house is b/c I'm a geology student and we use it to test rock types.

 

[littletankbigworld]

Okay. Good. And what about red lava rock? I think it affects the parameters in some way. And seashells raise the gH, I believe. Driftwood lowers the pH. Also, desert sand in some forms has rocks that will raise the gH dramatically.

 

[littletankbigworld]

So far:
ph gh
slate no effect no effect
black slate no effect no effect
granite no effect no effect
limestone
alabaster
lava rock
seashells raises
desert sand (some) raises
driftwood lowers

I know driftwood isn't a rock, but I just thought I'd include it. What do limestone and alabaster do to ph and gh, since you mentioned those?

 

[littletankbigworld]

Augh...I made that last post into a table and it all got shifted. Eck.

 

[emmanuelchavez]

Lava rock is pretty much inert, doesn't affect anything.
Limestones and alabaster will raise pH and gh.

Where did you get your desert sand from? The source rock makes all the difference. For example, the White Sand Dunes Monument in New Mexico is eroded gypsum. The type of sand you'd want to use in an aquarium should be primarily quartz-based.

 

[littletankbigworld]

I said "some" because I use Mosser Lee desert sand from Lowes and it has no effect. Before I bought it, I was reading about different brands of desert sand that raised the pH considerably. I suppose it would vary.