Is This Hith? (Geophagus)

[Joller]

it was a white dot about an hour or 2 ago but seems to be 'peeling' off, i've never seen something like this before. so please make suggestions as to possible cause, and treatments
weekly 25% w/c ph 7.2 amonia nitrates and nitrites read 0 ppm
kept in a 430L tank with 10 similar sized cichlids, no agression towards this fish from tankmates, still eating lots

pics

thanks in advance, joel.

 

[Joller]

it seems to have come off overnight but it will probably come back.
please help

morning pics, as you can see there white things gone and left a bit of a hole...