I wouldn't scrub the LR because you're going to scrub off all that is good and things you want. If it has coraline on it you could scrub it off, any bacteria could be scrubbed off, etc...
You could begin by simply plucking it off, there is way too much for the blenny to take care of. It's like having 3 miles of grass to cut and you only have a push mower.
Kill the lights for a while. Cut down on how long the tank is lit up, make sure there is no direct sunlight hitting the tank, if there is cover the part of the tank with something to stop it from doing so.
Check the levels of trates from the RO unit. If the media is old it won't continue giving you that quality. You could be getting not-so-good- filtered tap that still has all that junk in it.
I had that exact same hair algae 3 years ago. I fought with it for months before I just killed the lights completely for 2 months. The hair algae died off due to lack of lighting. All I did was pluck out the heavy parts as best as I could and unplugged my lights. Now I get small bits on the rear glass, but the Nass. and Turbo snails take care of it just fine.