True tangs need horizontal room moreso than the volume itself. The recommended minimum is a 4 ft tank length.
That said though without knowing your nitrate readings it's hard to say where to proceed from here. If you've been keeping up with the water changes/feeding and things are getting worse it could be too much for the tang to heal on it's own. The appearance of the tang definately suggest bacterial.
At this point I'm kinda leaning towards a combination of problems. The Fluval by the looks of the tank is the only thing moving water aside from the skimmer. That's only going to amount to less than 300 GPH
. The max rating for the 404 is 340 GPH
but that is calculated before head pressure and without media. If so, that about Â½ of the minumum recommeded flow for SW
. Combine that with the plastic lid and you most likely have a cronic pH problem which could easily result in acidosis. Your only reference to pH was made at noon (?) so I would be sure to repost what the pH is later in the afternoon.
I would definately suggest removing the lid completely and replacing it with eggcrate (see attached pic) and augment the flow with at least one Maxi Jet 900 (preferabley 2) or something of a similar velocity.
I think the best route for the tangs sake is to set up a QT
and treat with Maracyn II for seven days at double the dose each day. While the issues with the tank are resolved, the QT
being an open environment will have a better pH and the antibiotic will help if bacterial. Be sure you acclimate the tang to the QT
the same as any new fish. If suffering from a pH issue, a sharp increase can be just as bad.