Hi. I would be grateful for some advice. I'm new to fish. I think what I have is a common pleco. He's about 21cm long and 6cm wide. How many wafers should I feed him? They're about the size of a pinky nail and very thin. I've been giving him 4 twice a day and occasionally a piece of cucumber but he devours everything and I'd worried I'm not feeding him enough. Thank you very much.