Recently I've been noticing that my betta will occasionally, as in maybe a couple times a day at most, begin to swim on his side and he will get to about ~45 degrees before he corrects himself and begins to swim straight again. The incident only lasts <5 seconds, and he seems to be find the rest of the time, but I want to be preemptive in case it is something in its beginning stage.
I got him from Petco back in around October of last year. In terms of care, he is fed betta pellets and freeze dried worms (the kind meant for daily feeding), every other day, as in pellets one day, worms the next, etc. Except for Sunday, when I feed him half of a snow pea, cut up, and Monday, which is his fasting day. The tank does not have a heater, so it is room temperature, roughly 20 or 21 degrees Celsius (maybe a little higher) I'd say. I do a ~25% water change every ~2 weeks.
My guess is it's something wrong with his swim bladder, and I think maybe feeding him a snow pea today will flush anything out, as I've only started seeing symptoms this week. Any help?
P.S. A brown algae was appearing in his tank a couple of weeks ago. After washing it off, it seemed to be okay, but I am beginning to see small amounts of it again. Any idea on what it could be? I've been told that it is from nitrate, but I clean the tank, like I said, about every 2 weeks, so I don't think it's that.