I have a 10 gallon fish tank with 2 small african cichlids and a black skirt tetra. Because of a previous disaster, I got rid of the gravel, so don't have any right now. I am going to get some, but I just wanted to make sure that it won't harm my fish. I'm going to thouroughly wash it, of course. Also, is there any type of gravel or other substrate anybody recommends for these fish? Thanks. (BTW, I have a tank ready when the cichlids grow too big).