Glowlight tetra having trouble swimming - HELP!

I have a 10 gallon tank with 6 neon tetras and one platy (the other died recently of dropsy which I was unsuccessful at treating). I have been away in Spain for the past 10 days, and when I came back today I noticed that one of the tetras was swimming a bit on its side... a few hours later (now) I saw it on the bottom of the tank, upside down, trying to swim. A few times it has managed to get up and swim a little, but it has serious problems in doing so and soon returns to the bottom upside-down. One thing that I did notice is that many of his fins seem to have been possibly nipped by the other fish or something, as his anal and dorsal fins are smaller, plus his two front fins that he uses for propulsion (sorry, no idea what they're called) seem to be shorter - could this be what is causing him so much trouble?

Right now I'm not really sure what to do. Is it bad for him physically to be on his back like this, or should I just let him rest like this - I'm thinking that he's just tired because of the problems with his fins (making him have to exert much more energy to stay up) One thing: when I put my net in to try to see if I could get him to not be on his back, he promptly swam away... he keeps struggling up as I'm watching his right now, but after a few seconds he goes right back down.

Since he is always landing on his back, does that mean that it is a problem with his swim bladder, or what?

I really appreciate any assistance, and I appologize for any grammar/spelling/composition errors in here, I'm trying to get this posted as fast as possible.

After just watching him for a few minutes more, I realize that whenever he stops moving his fins, that is when he turns upside. So I guess that fish are just top-heavy?

Sorry about that, I just did the tests a few minutes ago because I realized that I had forgotten them... anyways, here they are:

pH: 8.0
Ammonia: 0.0 ppm
Nitrate: 8 ppm
Nitrite: 0 ppm
GH: ~6

budrecki said:

You water parameters are fine. If he is showing no outward signs of disease ( fungus, white spots, red spots) I would do a 75% water change and add melafix to prevent any secondary infection from the fin damage.

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Yea, I knew that the parameters were fine... but if they are fine, then why should I do a 75% water change?

So, it's okay that he is upside-down for long periods of time?

budrecki said:

Fresh water is always good if your fish are showing signs of stress.

No, it's not ok that the fish is upside down. Something is wrong. Make sure the water is pristine, that's all you can do.

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Hehe sorry if I phrased that wrong... I know that the fact that he's upside down means that something is wrong, what I meant was: will him being upside down cause other problems?

Absolutely.