Angelfish Disease Need Quick HELP PLEASE!!!

Question
Hello, I have  20 gallon aquarium with a black angelfish a 5 Von Rio tetras and
a few otos.  The tank is fully cycled and over a year old.  No ammonia nitrates
are low.  pH is a little high (7.5) for my South American amazon species, but
everyone seems okay.  I added this angelfish about two weeks ago and it
hasn't acted well since.  It hid behind the driftwood and only came out for
feeding.  A few days later, I noticed it seemed to have a little swelling behind
the pelvic fins.  I wasn't sure though because it is my first angel fish.  Since
then, it has gotten a lot worse.  It now hangs by the filter, doesn't eat and
breathes heavily.  I tried a shelled frozen pea but it wouldn't eat it.  Today the
swelling has gotten even worse, and now there is a white spot behind the
pelvic fin that looks like and injury, or the swelling is tearing it's scales! I have
no idea what to do.  Pleas Help!

Answer
Hi Corey,

Swelling can be a sign of various diseases, but a bacterial infection is the most probable cause, if the swelling is red and inflamed. The Angelfish may have gotten the infection from the store already, and the stress of transport from the store to your house made the fish even more susceptible to illness.

There is another probable cause. Is the swelling a pinkish color with some white spots? If it is, it's a goiter tumor. Goiters are caused by a lack of idodine in the diet. If you suspect that this is the case, adding a fish multivitamin (available at your local fish store, such as Sera's Fishtamin), will help. There are absolutely no side effects of adding this, so it's risk-free. If iodine is the cause, the tumor should fade away and disappear within a month.

If the swelling is red/inflamed/bloody: (Bacterial Infection)

If you have another tank, I would separate the Angelfish immediately.

Perform a 30% water change, and try treating with an anti-bacterial medication, such as Maracyn. The swelling should subside within a week. If it does not, it may not be a bacterial infection.

If you are not sure whether it's a Goiter tumor/infection, I would just use both the medication AND the multivitamin. Once again, there are no side effects to adding multivitamin.

Regardless of what path you take, add some aquarium salt. Add the salt, about one tablespoon per 5 gallons (4 table spoons in your case) during the water change. Remember to dissolve the salt first!

Good luck, and I hope your Angelfish recovers!