Another vote for poor water quality. If only one WC
per week with a juvie, it's safe to assume the tanks not getting wiped down or the filter cleaned often enough as well.
With a statement like "my water is fine" without allowing a test, as well as, it sounds like theres only one lonely 'ol Discus in this tank. Perhaps this person should'nt be keep these fish. Just my opinion.
Sounds like QT
is the best option. At this point, I'm not sure if this person having a spare tank for QT
is a good or bad thing on such a sensitive fish 8O