Backyard Aquaponics
A place to discuss aquaponics

I'm not sure what type of rock the gravel is. In my area I can get two different types that are both sold as base rock. One is from Syar in Vallejo, it is a bluish-green stone and it had the strongest reaction to the acid I put on it. The other one is from Cache Creek near Winters, it is a mix of many different colored stones, not all the stones in the mix reacted, but some reacted as much as the blue-green stuff.

I just looked up limestone on wiki and apparently it can come in many colors. It is often used as road base and is used to make cement. So it may be the stuff from Syar is limestone. I don't remember anyone mentioning problems with granite, so you may be ok.

Get a sample of the rock you are going to use and put some of it in an acidic solution. If it bubbles then it is no good. Also see if it is the crushed road base type of rock. If it has lots of fine particles, you may have to sift them out.

Little tiny bubbles?

Depends on what strength acid you put on it and how alkaline it is. I used pool acid. Some rocks I got huge bubbling with fizzing and popping, other rocks just small bubbles. With the rocks I deemed okay for use the acid just turned yellow, no bubbles.