what kinda rock?

[jbird79]

I was at the lfs and they had this rock that looks to be some sort of sand stone but i cant figure out what it is. It white and really lite. Ive looked through all the rock yards i could find. Anyone got any ideas

 

[fort384]

Sounds like aragonite base rock to me. For SW tanks...

 

[jbird79]

Its not base rock i got a pic i dont if u can see enough to id