Off topic ,but how is the fish doing in a 2.5 gal?I plan to get one in a 4 gal ,but I have doubts about the space.The side of the cube is 9.8 inches.
As for the algae ,I'd say lauralee nailed it.
I suggest a tank 2.5 gal or larger for bettas. You are doing a huge service by at least going 2.5, as a lot of people get those dang jars and cups, that hold like 2 or 3 cups of water. And then they do not change the water daily. Both my betta tanks are 3gallons or larger (the evolve four is actually not four gallons). Bettas are not entirely active, but they do like some space, despite common perceptions. I actually had two females in a 30 gallon at one point, they loved it (yes I know, not a good idea to have just two females, long story).
Also, I suggest a cheap escape tank in case of disaster. I have a little like 6 cup tank I keep handy for any emergency. And yes I have had to use it. I caught a mini-cycle that spiked my nitrites and ammonia in my 3 gal. Got the betta out right away and started 50% water changes for a week. It was worth the $5 for the little tank.
If you do not want to change water daily or semi-daily, get something with a filter.
I always wondered why large chain LFS have so many bettas, and seem to go through them all. I was like are people buying that many bettas? Then you see those under 2 gallons setups for sale on craigslist and know why.
To the original poster, yeah, 10 hours WAY WAY WAY too long, even with a cheap light. At this point 8 is prob too long now. I would go 6, possibly with a 2 or 3 hour break in the middle.
Clean as much out as you can, any plants way too infested prune, 50% water change and if all else fails, blackout for 3 days.
If you are using any kind of ferts, make sure you are dosing properly and do not stop. Stopping it the worst to combat algae.
