Interesting,never seen one like that before,I wouldn't mind trying one out.Though not sold commercially around here I have heard of similar units and they were referred to either as overhead or above tank filters.I suspected you were either referring to an above tank unit or a hang on power filter.While I'm not sure of the size of your topfilter I suspect that it isnt big enough to keep up with your fishes waste output....by themselves,rays are capable of producing large amounts of waste matter.
