I have read a lot of good and a lot of bad about phosphate removers. Since you seem to be doing a lot of the right things, I would look at your new lights and possible overfeeding as a source for the explosion.
My personal approach to 99% of problems like you have is to get something that eats it.
Emerald crabs love this stuff. I also had a rainford's goby that just tore up hair in my nano. With a 10 gallon nano, one emerald crab should do the trick, and he will eat other stuff once the hair is gone. Reef safe crab, better than a hermit for hair algae.
PS if you have flatworms, get a nudibranch. a velvet nudibranch will suck them up in no time. They only live for a few months, so it will die shortly but it will be one happy, fat nudibranch and will wipe out the flatworms.