Yep, I have hair algae from hell - all different kinds. All different kinds you say????? Yep, there's that green cottony stuff and I have Dersebia (however you spell it). Wowsers - that Dersebia can be scraped or scrubbed off or mowed down by tangs (apparently Tomini's don't like the stuff) off of frag plugs. If it's large pieces of rocks or frag racks then forget it. So what have I been doing about it. 1) large 25g to 30g weekly water changes (no changes) 2) weeding followed up with the above water changes 3) GFO (Granular Ferric Oxide) i.e. Rowaphos and now trying the Warner Marine Phosar stuff in dual Phosban reactors 4) The last is experimental - overdosing on Magnesium. There's a thread on RC that indicates that hair algae and high levels of Magnesium don't get along to the tune of 1600 to 1800 parts per million 5) Algae blenny apparently is doing very little to put any kind of dent in the stuff 6) The white spiney urchin I got from Alvin who got it from Dudley has done less except move my frags around the tank <grrrr> > Phosphates have tested at 0.25 or less (been testing every week). Nitrates are the same. I have tried the lights off for three days, and some of the tips of the algae turned white <still not dead though>. I typically feed frozen and dry pelleted food, but have gone back to using just pelleted food for a bit till I make a better dent into the algae problem. I have just turned off the calcium reactor and will be seeing if that makes any kind of dent as well - <excess co2 can cause algae blooms as well>. I will be dosing three part until all of this goes away. Luckily for me I still have (2 each) three quarter gallons of (2-part) B-ionic and just bough one gallon Kent's Tech-M. Skimmer was just completely disassembled and cleaned out via a dilute vinegar bath. I hope to install the skimmer back tonight. For those who have been keeping up with my tank know that I have two Tomini tangs that get relatively get along. I also have a rescue yellow tang that is currently residing in my sump while I am holding onto some other fish in my smaller tank. The yellow tang chows down on the algae like no one's business. I have been slowly adding frags into the sump area (since I was cleaning out the skimmer it freed up the large middle portion of the sump). I am so tempted to put the yellow in the main display to clear out the hair algae, but I fear for the Tomini's lives (they are all roughly the same size).