Depending on how you re scape that could be what started the issue. I know people who rescape with the tank full, do it in an hour and the lights on the whole time. I know others who are very meticulous and drain the tank, move fish to another home, kill the lights and filters (obviousy) and take 2 or three days to make sure they like it before re filling.
Anytime your light cycle drastically changes it can promote algea growth. So if you had no light for a couple days during the re scape and then turned it back on for the full 7-9 hours, algea blooms rapidly would start to develop. I would personally start there. I have many many tanks, all located in a room with blinds and that light has never been an issue!
Here's my advice.
Keep the light off for 4 days. Do 30% water changes all 4 days trying to suck up any of the hair algea possible, give a good glass scrubbing during one of the water changes. Add your oto's. On the 5th day turn your light on wit a timer and do 4hours on in the morning. Have the light of for 8 hours. And then 4hours on at night. This will allow the light to be on for 8 hours, but not straight. It breaks up the light cycle so you'll have better luck with the algeA.
Hair algea may take a couple try's to get rid of as it spreads so rapidly! But the 4 day blackout and new light cycle should help
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