I am slowly setting up a Axolotl tank. For the actual tank decorations I want to use rocks and wood from a local river. I find the idea of paying $6 a pound for rocks at the local pet store really unattractive. Since I have access to take rocks and logs from the river for free that is what I am wanting to use but I don't want to put anything dangerous in my tank. Can I just clean the rocks a great deal and use them? If so can I use any kind of chemical cleaner? Surely if I clean them until the very souls of the rocks are spotless they'll be ok to use in the tank...