No, it is definate nibbling, the plants are all very healthy and relatively new. both the barbs and shark are at them, usually overnight is the worst.
They are getting a good quality tropical flake food, they are keen to eat but usually dont finish it all at once, I am wary of increasing the amount in case I over feed them and cause any problems, is there anything else in the way of fresh veg or something that they would eat instead if it might be a dietary deficiancy?? I don't mind the odd bit of nibbling but it seems like I just turn my back and more leaves are shredded!

I thought of trying to feed just a tiny amount a few times a day, do you think this would help?