HI ALL, MY TANK IS DRIVING ME MAD. I HAVE A 7 FOOT TANK, 3 FT HIGH, AND RECENTLY CHANGED FROM GRAVEL TO SAND, SO GOT RID OF MY UNDERGRAVEL FILTER AND BOUGHT A CASCADE 700 EXTERNAL FILTER, AND THE WATER IS TERRIBLE UNTIL I CHANGE THE FILTER AND ITS FINE FOR 3 DAYS AND THEN BITS ARE FLOATING...