I just got off the phone with Motoman, he called me for some advice. I saw this thread earlier today but I refrained from posting because there was already so much (sometimes conflicting) advice I didn't want to add to the confusion.
Having said that, I told him I'd post my thoughts here in case he needs to refer to them again.
IMO he's dealing with a number of issues, so I'm going to address them in priority order.
1) Brooklynella. While this is sometimes referred to as "clownfish disease", any fish can get it, and many fish can carry it without showing symptoms (and then transmit it to others). Clowns are the most vulnerable to Brooklynella than other species.
2) Internal parasites. The stringy feces is certainly an indicator of that.
Motoman also mentioned that his grouper and tang are also starting to look distressed - scratching and color faded. There may or may not be something else going on.
Since Brooklynella can kill within hours, that is the first order of business to deal with. He's been unable to find Formalin 3 anywhere near him. He does have some Quick Cure which contains Formalin and Malachite Green, so in a pinch, that's what he's going to use in a 10-gallon bare-bottomed quarantine tank. He has a couple of extra tanks, so I suggested setting one up with 50% water from his DT, and 50% new water (to ease the parameter shift). I also suggested he needs some sort of biological media that is established, such as a sponge from the DT (or other bio-media) OR a "sacrificial" small piece of live rock (cured) to introduce denitrifying bacteria to the tank and help maintain water quality. This will NEVER be put in the display tank. Of course he'll also need water movement so aerator or powerhead or HOB filter with no carbon - he can decide what he can put together from what he has or has access to.
I also suggested treating the tang and grouper in a separate tank using the same method. In our first conversation he hadn't observed symptoms in them, but all fish can be carriers, so treatment is also indicated. Since then we've spoken twice more and he mentioned symptoms - I'd still treat them in a different tank since the symptoms aren't so advanced, and a 10g quarantine would be very crowded. I believe he also has a 20 at his disposal for those.
Assuming they get through treatment, *then* the internal parasite issue can be addressed if it's still present. This is something that needs to be dealt with, but since mixing medicines is contraindicated, he's going to have to tackle one issue at a time. Internal parasites are problematic in the long term, but in the short term the Brook is the most urgent matter to be dealt with. If the fish get through the Quick Cure treatment, then in new water (free of other medication, and after a few days' "rest" from medication) he can address the internal parasites either with Metronidazole & Focus OR PraziPro - both are suitable for deworming.
He mentioned he was on his way to the LFS for some Prime (for the other QT that has ammonia that won't be used for this treatment) - I also suggested he get Stability to help with the water quality in (all) the tank(s). I also suggested he see if they have Seachem Paraguard to use instead of the Quick Cure if they have it. It's not my preferred medicine against Brook (Formalin 3 is), but it is supposed to be effective. So whichever he ends up with will be better than doing nothing.
Having said all that, we also discussed fish choices for a 33 reef. I would not have suggested a boxfish, which perished a couple of months ago (bought the day he moved the tank). Boxfish aren't reef safe and they pose other risks too, which were mentioned earlier in this thread.
The grouper is also not a suitable reef tank choice, particularly for such a small tank. He may be small now, but they grow quickly, to about 30" (I had one that was about 18-20" in our 1000g when we had it).
The blue tang is also not a suitable choice for such a small tank. This fish came with the tank but it does need a larger home. It is reef safe, but needs much more swimming/grazing room.
And finally, 3 clowns - also not recommended. He mentioned there was one mated pair and another individual. In my experience a pair will harass a "third wheel" right to death. One pair per tank. Even if he moves them to the 210, there may still be territory issues. Best to pick the pair OR the individual and not both. And of course eventually the grouper will be large enough to make them into hors d'oeuvres.
Hopefully he gets his QT sorted and treatment started before it's too late. Brooklynella can move very quickly, but for his sake, I hope he gets treatment going in time.
Jenn