Whoa, people, wouldn't putting in 2 snails (one per side), or putting in 2 Ottos (catfish? i assume) overstock a 3 gallon tank that already has 2 bettas in it???
I agree with Sushi67, you could buy some liquid algae killer like those seen
here! I've used the "Algae destroyer liquid advanced" before, and it worked fine for me.
I would also suggest investing in an algae scrubber
brush (especially one with a handle), instead of one of the hand-held pads, the brush makes scrubbing the algae off very quick and easy. Just run that along the sides of the tank as often as needed. I'm not sure how that would work on real tough algae, though, a brush gets mine off easy, but so would a paper towel.
IMO, a little bit of algae is good, gives the tank a "lived in" homey look, but too much is just trashy.