i am currently getting all the supplies to make a 29 gallon tank for a bunch of different fish, gourami's koolies, corydoras ect. and was wondering what substrate i should use. i have gravel, but want something softer for the koolies to burrow in. what about sand? what kind of sand is safe for fish tanks, and is it sand you can buy at home depot or something, or is it "fish sand?" thanks!