And otos will munch diatoms all day long
Obviously you can't not do water changes, so have to look at other factors. I would do 50% on my planted tanks regardless as the benefits do outwiegh any cons with tap water.
I suggest giving this a go- do a 50% water change, give everything a good siphon and clean, especially the algae.Stop dosing any plant products like flourish, decrease photo periods by maybe 2hrs, and feed lightly. After a week I'd say you would see an improvement,