Rasbora infections after injuries

[Maggie]

My rasboras get into constant scuffles. The males constantly flair their deep orange dorsal fins and go after each other and the females relentlessly. I am sure it's because I don't have a large enough group (started with 8, lost one to injury) for the 45-gallon tank they are in. My 5-gal q tank is really insufficient, so I decided I can't get any more fish until the 20L is set up and the 10 can be q tank, and it will be next week before that's ready. I want a couple of other kinds of fish but think more rasboras needs to be the priority, for their health. I'm going to get 10 more and think that would make a nice group of 17 if everyone survives this ordeal, whatever it is. 

Anyway, one was injured in a fight a few days ago and I waited it out to see if it would heal. Well, it didn't. A white fuzz started to grow in the injured area, which quickly spread. Another fish got fuzz on his back behind his dorsal fin. I'm not sure if he had an injury there, but it wouldn't surprise me. Both were also swimming erratically, including turning upside down and floating as if they lost control, and then shaking it off and going back to normal swimming. They also started not keeping up with the group and staying off by themselves more often and lower in the tank. Monday night I started treatment with erythromycin and API general cure. I'm pretty sure it isn't ich since there are no well-defined white spots, but if anyone thinks it could be, please let me know! The fuzz on this one whose right "side" fin (pelvic fin?) was injured now also has the fuzz is under the left side fin and body. Today, thankfully they both look a teeny bit better, they both ate breakfast, and I'm cautiously optimistic. I can't get good pics as they are all very nervous and do not like the medication at all. I can't locate 2 of the otocats but will do a thorough search today. It's almost impossible to find them even with a magnifying glass!

Water conditions: pH 6.6, temp 78, Amm, NO2 both zero, NO3 <20 ppm. I do 10% WC 2x/week and use API stress coat dechlorinator along with aging the water for several days, and heat water to match tank temp before adding. Haven't measured GH or KH recently, but KH is raised some using wonder shells (both 89.5 ppm without wonder shells, and pH crashes without them).

[Maggie]

Did 25% WC and remedicated. One more dose of erythromycin tomorrow and hopefully will be done. The two sick fish are doing much better today! They’re all swimming together, nobody is swimming severely erratically, and they all ate dinner. WC wasn't too traumatic either.