I have one Yo Yo...I bought it to get rid of some snails in a small 60L tank. I intended to put it in my 5' tank once it got rid of the snails but it paid the snails no attention at all. Eventually I had to move it anyway as it was driving the fish in that tank nuts. (small tetras). Now its in the 5' with a bunch of angel fish and tries to bother them all the time. They seem to just ignor it but I wonder if Discus would be so forgiving. I was going to get some more yoyos as I believe they are happier in groups but im not sure with its boisterous nature that I want a bunch of them in there......