I am chnaging my substrate to sand in the next few days and i read in one of my books that you can use an UGF as a return from your external filter so that the substrate has a current going through it. Can this be done and would it work with sand? I am wondering whether this would stop waste food settling causing problems with it rotting. I am thinking it would be similar to the uder gravel jets i saw a thread on here about last week.