Thanks April , I've got a biowheel attachment for my Magnum so will swap that over . I've got an 80gallon they can go in - and was reading that if I throw some driftwood and decorations and they have some spaces to hide they'll feel more secure .
Will try out the Aragonite . 18 2"baby discus in an 80gallon should still maintain growth with 2 water changes a week?? Any advice - 90% change in the 20 should equal 2 changes a week in an 80 gallon?