hi all, one of my res (who likes to spend nearly all his time in water) seems to have a spotty light-greyish sticky substance around his neck. more precisely, its located around the skin folds near the base of his neck. i havent been able to remove it, but it doesnt seem to bother him.

i checked the water quality, and its excellent. its a couple of days before i do a partial water change, but his tank is slime free as well as his river rocks.

any insights?

thanks