What I do, Is i just take the tiles off the backing, and slide them up right against each other. If you are not housing anything in your tank (which I think you are) you could grout the tile. I have never done that, so if you do that let em know how it goes. As for cleaning the tiles, get a pair of tweezers, the kind with bent ends, the lift up one of the tiles. The other tiles will be simple to remove after that.