Hole in fish

I came home today to find that my fish has a hole in her side. I noticed a bump yesterday, and was going to keep an eye on it, but today it's a hole!
Here is a picture: http://i37.tinypic.com/sxn6u8.gif
That's about as good a shot as I could get.

Some time earlier this week, I noticed she was holding her left "flipper" fin (the proper term eludes me) in place and not really using it to swim. I figured it was because she was in the middle of a turn, but I have seen it constantly in the past few days. It's intact, she just hasn't been using it.
On the same side, yesterday, I noticed a bump had formed where the hole in that picture is - so I don't think this was caused by another inhabitant of the tank (at least not originally). Today, it's a raw-looking hole.

I also found one of my neon tetras dead when I came home, stuck to the filter intake. I don't think the incidents are related, because this neon was old (3-4 years) and had previously been ill, but I'm open to the possibility, although their symptoms are COMPLETELY different (neon had pop-eye).

Other tank inhabitants (signature is inaccurate, will fix soon):
3 other danios
3 neon tetras
1 betta (added Wednesday, completely ignores all other fish)
A bunch of snails and plants

Parameters are normal.
Ammonia - 0
Nitrite - 0
Nitrate - 20-40

All the other fish are bright, alert, and eating normally. This danio has been eating all days prior to today.

I have her in QT now, and she's just sitting on the bottom of the tank. She was swimming when I found her today, but didn't look very good. Now she just doesn't look very good.

What should I do to get her back on the road to being a healthy fishy?

Edit: She just started swimming around in QT. It looks like she's having trouble staying up, and her nose tilts upwards while she swims. She is level when resting on the floor. This started after I put her in QT.

sed03f said:

Is this a 10gallon? The danios will probably pick at the bettas tail

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Yes. The danios have ignored him completely thus far. I was concerned about that as well, and have been keeping a close watch on them.

sed03f said:

I only say that because I had the exact same # and species of fish in my tank about 6 years ago in my first 10 gallon.
I had a dojo with an open wound like that a few months ago and he healed, but still has lumps all over him. I think he has cancer or something. But, no I dont know what exactly it is. Quarantining him is a good idea. Maybe try some parasite remover or some antibiotics if he doesnt get any better. Some aquarium salt couldnt hurt either, but dont try it all at once. Keep us informed

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I think I got lucky with this betta. He's gorgeous, completely ignores my snails, and so far, has had 0 incidents with the other fish. Anyways, yeah, I have a mother hen's eye on them.

I was wondering if maybe it was some kind of parasite, because it was a bump yesterday and then it ruptured or something, but I haven't seen anything that looks like it might be parasitic. Any brand you'd recommend, in case something does turn up?

sed03f said:

no, I have to use wardleys ick out sensitive for loaches, I dont recommend it, it requires oodles of water changes. You could always start a new thread

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lol, I'll keep that in mind, then.
I probably will if I see anything that looks like it's eating my fish. Right now all I have to go in is a bump that turned into a hole :/

DarrylR said:

Is that a Giant Danio?

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No, just a danio. She's 2 or 3 inches long.