I don't know the specifics of your setup,here is everything that can lead to high nutrients levels that I know of.
Overfeeding,overstocked,lighting,water source,filtration.Only you know if one or more of these are related to what's going on in your system.
overfeeding...reduce feeding,switch to frozen may help
overstocked...I don't know how many fish you have,but maybe your system can't handle the load.
lighting....sometimes reducing the lighting period may help,replacing old bulbs too.
water source....tapwater is bad,try switching over to RO/DI water instead
filtration...if pads,media are not replace regularly they can be traps for nutrients that is feeding the algae bloom.
Those are the only ones I know of...I hope something there helps.