Hi all,
There are quite a lot of reports of them doing this sort of thing. My suspicion is that it is when they are really starved, and it is a last gasp response to suck on anything soft. The range of algae they eat is quite limited, and is basically the diatom and algal sporelings in the biofilm, that is algae that we don't recognise as "algae". All the green thread, BBA, GSA etc that you can see is of no interest or food value to them.
I've had some of mine for several years and they have never eaten any form of algal wafer, or any other food, or shown any inclination to attack other fish.
What they do eat is the cucumber, melon, green bean or courgette that I put in for them, and presumably any diatoms that they can find in the tank. They like the vegetables when they are starting to go "slimy", also as they have grown older they have become almost exclusively nocturnal.
cheers Darrel
