Corys with lumps

Right folks I'm in need of help.

Tank - 5x2x2
Fish - 8 Geo tapajos, 9 Bronze cories, 4 juvie Rotkeil sevs, L240 plec, L318 plec

Problem -
For some time I've noticed that one or two of the corys would get large whiteish spot type things around their fins. They would occasionally flick, but eventually the lumps would clear up and all would be well. I put this down to the l240 having a bit of a gnaw at them at night maybe if they went into his cave (he's very possessive even though he stole it from a geo)
Anyway, I've looked into my tank today for say the first time in a week and ALL the corys are covered in these lumps all over their bodies. The lumps almost look like wooly popcorn and fall off when they flick which they seem to be doing a lot. They're a lot larger than whitespot lumps too, very strange....

Any ideas what it could be?

try treating them with ick guard then water change and add some aquarium salt to the water after a 3-6 days do 2 more water changes then the next week treat them the same way when u see it all gone do a 25-50% water change