ok, so these rocks arent in a river but are probably from a river... there is a 7 foot pile of round rocks at my friends house and he told me that i could take what i wanted... also he has a quarry at his house that has been filled with water since i can ever remember (23 years at the least) that has flat rocks all over that i could probably use
precautions, thoughts, ideas, pictures of what other people have done???
if they fizz when vinegar or acid is dropped on them then they are calcium based rock and will probably increase the PH of the water. Limestone and sandstone are common examples and are often found at the beach.
Most smooth black coloured rocks are granite and is fine. Most rocks sold as river rocks are fine as well.
The main thing to be wary of is chemical contamination of the rock. Places that handle these things quite often transport them in containers that have had all sorts of stuff in them. Chemicals etc, could have gotten onto the rocks and might leach off into the water. Also if there have been chemicals like herbicides used in the area recently then it could contaminate the rocks too.
Rinse the rocks under tap water and then put them into a clean bucket of water and change the water each day for a couple of weeks. This should remove any trace of chemical contamination.