Just an update-I gave the fish a semi high dose of Furazone and Metronidazole. All of the fish except the biggest cow have responded very nicely. All of the raw areas look normal now, and they are back to their old selves. Lots of fighting and posturing. The big cow has just a touch left, and it should be gone in another day or so.
I've been changing water 25% every other day, and I have been monitoring the levels. Ammonia, Nitrite, Nitrate, etc. looks good. I think maybe the problem was what I was feeding them. Most of the time, they get either raw shrimp, salmon, tuna, or squid. One time I fed them channel cat filets, and they went bonkers over that stuff, so I switched over to that for a month. Maybe the stuff was bad, especially since it's from freshwater? I went back to the shrimp today, and I soaked it with Vita Chem first. Since I didn't feed them for a little over a week, they just inhaled the food.
Thanks everyone for all of your help!