sick oscars

Question
I have a 55 gal tank with (now) 2 Oscars. one has a sore on its top fin and keeps getting bigger it also look like it has sores on its lips. they are both black with orange stripes but are a grayish color.what should i do?

Answer
Hi Rod
I just saw this section on all experts, didn't realize there was a pending section.  Usually the questions are given to me.  Hopefully it's not too late for your guys.  

I want to start out with one oscar should have a minimum of 55 gallons.  For 2, it's recommended a minimum of 75 gallons.  The reason being, oscars are messy eaters, and the nitrates in a tank with them can go off the wall.  Not to mention they do grow large, 12+ inches.  I had one that was 14.  There's barely enough room for them to turn around in a 55 gallon tank.  

As for the sores, are they fighting?  That would explain the sores on the fins and lip.  They could've gotten infected with a bacteria as well.  I'd recommend adding a little aquarium salt to the tank, dose at 1 tablespoon per 5 US gallons.  Also probably a good idea to pick up an antibiotic.  I would try some Marcyn Two.  It's great from gram negative bacterias, which is more common in fresh water tanks.  You haven't noticed any white stringy material hanging from their mouth or bodies?

Also be sure to do frequent water changes, with 2 in that size tank, I'd do 30% every 3-4 days, being sure to vacuum the gravel/substrate well.  Also remember with salt, salt doesn't evaporate with the water, it's only removed when water is removed via water changes.  So keep that in mind when adding new salt.  

Hope that helps and good luck!!

Christy