The things (that I remember) I did to try and beat bryopsis - which is the most tenacious hair algae there is:

Rinse all food in RO/DI
2 Phosban reactors
Ozone
UV
No light for 3 days
Increase Mg to 1800 (tried this TWICE - with no result)
600 - yes, 600 turbo snails
20 lettuce nudis
Direct application of kalk paste
Rabbitfish (I had lots of different tangs)
Lawnmower blenny - right...

What worked? Well, I tore down the tank (215 gallons) and managed to kill off all of my sps. Including some real trophy colonies... Bleached the rock for a month, then sat it in fresh water on the deck for 2 more. When I tore it down, I hooked my lone remaining Hiatt filter. I KNOW that I didn't get every piece of bryopsis - there's no way. But none has come back. I don't know if it will work or not - but it is a nutrient removing beast.