About a month ago, I bought two little fiddler crabs and put them in with my betta. He was extremely curious about them, but after a while left them alone. And they were doing fine. I had a large plant that one crawled to the top of, and got the idea to make a sort of paludium for them. They were doing fine and even shed their shells once. I thought about making the surface area larger so put a piece of wood near the top of the aquarium. This was treated and I've used it before in my other tanks. The only problem with this piece of wood is that it leaches into the water and turns it a dark gold color. I've been told that this has no harmful effect and is actually beneficial for fish. I've had fish who've lived in this type of water, so I don't think it's of any harm to them. But what about crabs? I came home yesterday to find both of them dead, which leads me to believe something killed them at the same time. I'm wondering if it's whatever leached into the water from this piece of wood. Has anyone ever had anything similar to this?