rocks in a fresk water tank

Question
I just set up my fresh water tank.  I want to put some rocks in  it that I got out of Puget Sound, being that the Sound is part of the ocean, is it safe to put those rocks in a fresh water tank.  Would boiling them be enough to make them safe for a fresh water tank.  Some of the rocks are either coal or volcanic rock I think.  I have and old spiral shell about the size of my hand that I got out of the Gulf of Mexico that I boiled and put in there and everything has been fine.  If you have any information I would appreciate it.  Thank you    Jason

Answer
Hi Jason,
Boiling, rinsing and scrubbing should be pretty effective to remove residues from the rocks. I've never used Coal rocks in my aquariums but according to my research sometimes they can be unsafe if they are treated with an oil-byproduct to reduce the dust. Volcanic rock is safe though. And it is often used in filter systems including pond filters.

You might want to do the vinegar test with your rocks to test how much they might alter your water chemistry. Putting a drop of vinegar on the surface of the rock and watching for any 'fizzing'. If it bubbles then you likely have a rock that is going to leech out minerals into the water to make your pH higher. You could also put the rocks in a bucket of water and test the pH then and a week later after the rocks have sat in the bucket. It's not a really big problem but some fish don't appreciate such a high pH. And its best to limit those kinds of rocks as much as you can.

I hope this helps and best of luck!!
((I'm sorry for the delayed response... My internet completely went out and I just now got it back today-- Friday Jan. 16th))

Karen~