i was a tad wrong on the stress, but it could have been because of the tang.
the 20 gallon would be better as long as you clean it insanely well. read the following and see if you still need to set it up, but it wouldn't hurt.
from the disease forum:
Popeye is also known as exophthalmoses or exophthalmia. It is more of a condition than a disease. It appears as an extruded eye where the eye socket is out further than normal, it can also be accompanied by cloudy eye if a pathogen is present. All this equals an eye trauma. It is not contagious. Even with these symptoms the fish can still appear to be healthy baring any pathogen that may be present. A pathogen is: a specific causative agent (as a bacterium or virus) of disease.
It is normally caused by environmental conditions like poor water quality, high DOC’s, high nitrates, improper catching like when using a net, fighting with other fish, or by having hit something hard in the tank like rocks, heaters, or any other stationary object. It can also be caused by bacteria, parasites, virus or a growth behind the eye.
In minor cases of Popeye the eye will usually return to normal without blindness. If more serious the eye may appear colorless, grey or have that clouded look, and could result in blindness in the eye. If both eyes are affected and are severe the eyes may burst or disappear in which case the fish may not be able to recover and may die.
Treatment: Overwhelmingly it appears that the first step to take is to do a large water change. At least 30%. This can be done in the main tank with fresh saltwater that has been vigorously airiated and mixed for at the very least a 24 hour period, using 2 or 3 day aged water would be better. Raw saltwater,freshly mixed and not aged and aerated is stressful to fish and highly irritating to sensitive gill tissues. Why the water change? This will help remove DOC’s and Nitrates and improve the condition of the overall system, providing a cleaner and healthier environment for the fish to recuperate in, quite possibly removing that condition which caused the Popeye in the first place. In most minor cases the injury will heal itself, however it also depends on what caused the condition in the first place.
The second step is using meds. Typical meds used for Popeye include: Melafix, Maracyn-Two, and Nitrofurazone. I have also seen where Kanamycin sulfate and Neomycin have been used, as well as Tetracycline and Chloramphenical. I won’t mention copper.
If meds are the answer then all the rules of the Q-tank apply, and for around 50 bucks your in business with a QT. If you don’t have one, do it now.
If using meds like antibiotics then you must QT the fish. Antibiotics are not always safe for inverts. Some can kill the zooxanthellae that live within the tissues of photosynthetic animals. Not a good thing to use on crabs, snails, corals or your sand bed.
Maracyn–Two or Nitrofurazone are the two meds of choice here.
Treatment: Using Maracyn-Two; Maracyn is Minocycline and comes in fresh and saltwater formulas. Both are the same medicine with one exception, the saltwater formula contains B vitamins that are hard to consume when the fish is exposed to the antibiotic, thus the addition of the B vitamin. A broad-spectrum antibiotic for internal or external gram negative bacterial infections. Effective treatment of fin and tail rot, popeye, gill disease, dropsy, bleeding or red streaks, secondary and internal infections. Effective even when fish won't eat.
Use the Maracyn-Two at the double dose each and every day for 7 to 10 days if the infection appears to be internal, 5 to 7 days for external. A small water change before each dose is recommended because the organics in the water can inactivate the antibiotics.
NITROFURAZONE is bactericidal for many gram-positive and gram-negative bacteria causing disease in fresh water and marine fishes. This antibacterial is effective for control of Aeromonas, Vibrio and related species. Nitrofurazone is particularly useful for control of minor topical skin infections of marine fishes that have not become systemic (internal).
Using Nitrofurazone (Furacyn): Dose 30 to 40mg/gal in quarantine only. Dose on the first day only and leave the fish in the treated water 3 to 5 days. Feed lightly.
