OK, I have a 10 gallon fresh water tank that has been set up for about 3 months. My Mom had about 50lbs of natural slate in all different shapes and sized that came from an old tank someone had given her years ago. She had the slate stored in her cellar for quite sometime. Anyway, she let me take what I wanted of it and I set up a cute little cave like swim hole for my redtale shark. He loves it. My question is, it is safe to keep in a freshwater tank. I did wash it really well and boiled it before I put it in my tank incase there was anything on it that could harm my fish. Everything seemed to be ok, but today my pleco died. The slate has been in the tank for about 4 days now. I am also having a bit of touble with brown algae growing. I have been doing a water change everyday and keeping my light off. I know the algae wouldn't have killed the pleco, just wondering in the frequent water change or the slate killed him? Anyone have any advice? Thanks for reading.