I found some stones outside my house that I would like to become part of my 20 gallon long build. I have placed the rocks in a bucket of water and monitored for pH changes over several days. The pH remained stable. Vinegar test was also negative. Are they any noxious substances that could leach out of the stones I should be concerned about. I have no idea what the composition is. The stones have had a 10% bleach bath and copious rinse.