River rocks in aquarium

[Mookka]

I was recently doing some whitewater kayaking down on the Potomac river when i stumbled across so really nice rocks! I have boiled and baked all of them twice and i was wondering if there is anyway to tell if the will alter my water chemistry?

 

[blueturq]

If you add a bit of vinegar to the rocks, and it starts to bubble up or fizz then it will alter the pH of your water, if not then it won't!

HTH

 

[Brass sliver]

Make sure that no metals are present. Put them in a bucket of water for a few days if they rust or have veins that do dont use them.