Well, as I mentioned, the "science" of sea salt is so untrustworthy that I really can't swear any one salt is better...so it's prolly really irresponsible of me to make such a suggestion, but...I wonder if Red Sea salt is my problem. My detective story:
I've had a similar algae problem for some time. It's not what I think of as "hair algae"--coarse, filamentous green stuff--but rather more a slime algae and diatom sort of problem. Only hairlike/fibrous structure visible is on a very small, closely-viewed scale. Typically dark brown, with some patches of red (the red stuff is especially slimy, I suspect it's cyanobacteria.
This began right after my tank crash. At first, I thought I'd simply destablilized the balance of algae in the tank with the crash, but now I'm not so sure. I did massive water changes after the crash, of course, so I started to think that perhaps my prefiltration system was letting enough critical nutrients through that, with massive water changes, I concentrated too much nutrients in the tank. Theoretically this would mean the algae bloom would go away with time as the algae gobble up nutrients and I siphon away the alge. But it's persisted.
Right before the tank crash, I'd purchased a bucket of Red Sea salt on a great sale at Petco. I'd been using Instant Ocean previously with no problems. I'd started using it gradually, mixing portions of IO and Red Sea, mostly just IO. After the crash, I was low enough on IO that I used much more Red Sea. Quite possibly, then, my new algae problems are in fact the result of switching over to mostly Red Sea salt.
The algae don't seem to be HURTING anything, so I'll live with the problem for now, but I'll be trying some new salt when it comes time to buy again. Would anyone have suggestions on salt? Colin, I know, is very happy with Tropic Marin...I was surprised to find that I can order it affordably online, even after the steep shipping weight charges. I did some searching and found much discussion on salt on Reef Central. Quite a confusing mix of information there, but I walked away with an impression that Crystal Sea Marinemix Bioassay might be worth trying. Any other ideas? I don't mind trying something new, though I seem to know of at least one mix (Instant Ocean) that seems problem free for me.