I went to one of the LFS today and brought 8 fresh water mussels, apparently they filter the water and put some type of foot into the gravel helping to keep it cleaner? Does anyone use them in discus tanks? You must have gravel for them to live in. Only one of my tanks has gravel in it and I have to say it is the one tank I have no trouble with and the fish are always laying. However I would like to cut the water changes down from twice a week to once a week.