A fishy night

I started keeping fish a couple of years ago. I have always like small community fish and we bought 120ltr tank which fits in the alcove by the fire very neatly. We have relatively easy care fish plus my rather large Catfish. He was purchased to keep the algae under control ,a job he has done reasonably successfully. However I read on Google that most fish of this type need a much more varied diet than just algae which explains why they do not grow to their normal size in many aquariums. So I have been feeding this one on cucumber and he loves it . He is now a magnificent specimen and devours a snack cucumber every day. Chris says Ishould put him on a diet.