relies upon very much on what style of fish/animal you have in it, what number, how huge the tank is, what style of clear out, and greater. maximum individuals advise gravel via fact it extremely is yet another place for sturdy bacteria to enhance. some fish prefer sand to dig in, so substrate is a would desire to. on the different hand, in case you have something extremely messy, which includes a turtle, or a sort of fish hassle-unfastened for ingesting gravel, then gravel is a no-no. no rely what you nevertheless would desire to hoover the backside of the tank, whether there's no gravel gunk will pass to the backside. I choose gravel in fish tanks via fact in my opinion i think of evidently greater effective.