Hi!
When I had hair algae really bad, I would have a series of rinse buckets. I know this sounds anal but any free floating algae that goes back into your tank has to settle somewhere, and its usually somewhere new
I had about 3-4 buckets of SW (whether it be new water or the changewater from your tank). I would scrub in one, rinse and scrub in the second, then rinse and rinse. As the first bucket got yucky I'd dump it out refill it and send it to the end of the line. I had quite the little assembly line going for awhile there.
As for the 50% water change, I don't think its unreasonable. However you may want to look at what is fuelling your algae problem. Do you use RODI?? If not you may want to look into it to reduce any added nutrients coming in from your water change.
Other things to look at to reduce algae include:
increased skimming
increased alkalinity
adding a refugium
Hope that helps. Good luck with the war on algae. It almost did me in
