About 3 months ago we started seeing evidence of "hair algae" (please don't ask me to identify the species) in our 150 gallon. The system had been running since last September with most of its rock and livestock coming from a 55 gallon set up that my 17-year-old son kept. He had battled HA in the 55 for several months before the move but seemed to have it under control. We have a very diverse coral collection from sarcos and singularia, ricordia and other mushrooms to SPS and LPS, cyanarinas, blastos, micros, zoas, etc. Also a diverse clean-up crew with a bazillion snails of about 5-6 different species, hermit crabs.
Fast forward to Feb/Mar...we started seeing the beginning of HA. Since all our test results were good (Alk 8, pH 8.2, Calcium +/-400, 0 on nitrate and phosphate), I am very faithful with maintenance (clean skimmer and change filter sock 2X weekly, monthly water changes) and I rinse frozen food and feed very lightly, run gfo and purigen...I was really surprised. I'm still not sure what triggered it, perhaps the disappearance of our couple year old lawnmower blennie a couple months earlier. Anyway, I manually removed as much as possible, but like many folks I just succeeded in spreading it around. I tried the usual suggestions (+ mag, lighting schedule, wet skimming, etc.) with no result.
I dosed for the first time May 28 (Thursday). Everything looked good when I left town Friday. Sunday evening I came home to a totally bleached acropora valida and pink birds nest. I don't know if something else could have happened (a temp spike?).
Most of the HA was dark and pulled off quite easily. I think I miscalculated my system volume trying to estimate the water displaced by the rock and overdosed. I waited until June 9 (this past Tuesday) and dosed about 1/2 my original dose. Once again the HA is showing signs of deterioration with no adverse effects on any other livestock. Crabs, cleaner shrimp, snails, fish, other corals all seem to be okay. My two largest sarcophytons aren't totally happy, but it could just be their time of the month...you know how they are.
I plan to continue to use this product but want to caution folks about dosage. If you aren't SURE of your system volume, I'd suggest to dose at a lower level than you might think. Remember that most of the rocks are porous and there is a lot of water filling in the gaps between the rocks so don't do what I did and just think, "if I piled all the rocks up on one end of the aquarium, would it take up 1/4, 1/3 of it???" I don't think that is a good way to guestimate. I might sound like an idiot for even saying it out loud but surely I'm not the only one that thought that was a good idea

at the time.
Thanks to everyone that posted their comments, I never would have tried the product without your experience. I wanted to post my experience in hopes I can help save someone else some heartache.
Happy Reefing!
Keaton's Mom