pectoral fin and breathing problem -- fungus?

[Tostada]

OK, I know this picture is terrible, but it's all I've got:

I had a rasbora about 3 weeks ago (the above picture), one of my smaller ones. Its right pectoral fin seemed to get really thick. I thought that it had been nipped by another fish and was damaged or something. The fin didn't move, and the fish had a little trouble swimming, but was mostly fine. Then after a couple days it had a lot of trouble swimming and died.

A couple days ago I found another rasbora with the same problem, except this is my largest rasbora, and this time it's both of the pectoral fins. It's still able to move the fins, but is having trouble breathing -- its gills are moving very fast. I can't see any fungus on the gills, though. Really, the only thing I can see is that the pectoral fins are thick-looking and much more visible than any of my other fish, and the fish is twitching its gills spastically.

 

[Devilishturtles]

Kinda sounds like a bacterial infection, possibly columnaris. I would watch for anymore signs ot illness. If you see any, I would treat the tank with Maracyn-Two or Tetracycline as soon as possible.

 

[Tostada]

Well, the 2nd one died before anybody replied. Now a 3rd rasbora has the same thing on one fin. I'm going to go get some Maracyn-Two.

So, I've got a fully-stocked 30 gal. hex where the rasboras are, and I've got a 5.5 gal that only has a betta and 3 baby dwarf platies. I could probably manage to rearrange things to use the 5.5 gal for a hospital tank, but if this is a bacterial problem shouldn't I just treat the whole 30 gal. to make sure the fish in there don't keep getting infected?

I don't see any FAQ or articles on treating fish.