I have a new 10 gallon tank with 2 guppies, 1 clown loach, and a male betta fish. My betta is flaring his gills, and looks like he's trying to bite me if I turn on the light, or go up to the glass with the light on. I've had one previous betta before and never has done this. I'm really concerned he is scared or something.
Please help me... and my fish!!

To my understanding betas are not meant to be in with other fish. You should remove him and put him in a separate bowl.

I have now put him in another tank with tetras and plecos... is this OK?

Our animal experts aren't on at the moment to answer you. They will be. Then they can properly answer you.

I use own betas, and I always kept them by themselves.

I would put him in a separate bowl until you get better advice.

Strange... ive always had them in tanks with other fish but he seems to be fine with the other tank curently

They are an aggressive fish, ( although I understand a poor fighter ?) They are normally sold to be in tanks by themselves. I have always keep mine in their own tanks

http://www.aquariumguys.com/betta-fish-care-article.html

They can be put with some fish
http://www.better-bettas.com/a/compatible-with-bettas.shtml

Male bettas will try to fight and kill any other fish with bright colors, especially ones with large tails.

Having them in a tank with other fish can really stress them out, sometimes to the point it can kill them.

If you can I'd separate him completely, they don't need huge tanks and if you keep a small tank in a warm room you don't even need a heater.

Really enjoyable fish, we used to hold a mirror up to the tank to get ours to flare up occasionally... sounds cruel yes, but it's actually good exercise for them.