When it happened to me it was because I left my skimmer off for a period of time. I am not an expert by any stretch of the imagination but I believe dissolved organics from fish poop and anything else like uneaten food etc. makes the water oily and the oil tends to float and be caught up in the surface tension of the bubbles your skimmer makes. once the skimmer has gotten a lot of this built up stuff out of the water it should calm down. someone more experienced can probably explain it a lot better but that's my basic understanding.
About 1.5 years ago I was kind of where you are now. (ok not the exact same circumstances but Phosphate control in general) Tank was about a year old and I had a lot of hammers, forgspawn and other LPS and soft corals that were doing well, but I also had pretty high phosphate that I couldn't figure out the best way to control. I could not for the life of me get a fuge right no matter how many different rearrangements i tried (i DIY all my filtration pretty much) I ran GFO in a reactor for a while and ended up with a nasty crop of dinoflagelates. The piece of equipment that let me take the next step was an algae turf scrubber. People have success with plenty of other methods that's just i chose to try. And i'm a big DIY guy, but there are plenty of commercially available options too. Hair algae uses a ton of phosphate and nitrate (chaeto only really wants nitrate) and IMHO its a process that wants to take place in your aquarium and use the nutrients up... why not take advantage of it? If you do decide to try it and go DIY, here is a great site with guidelines that will help you make a functioning unit. Don't guess on sizes and ratios... there are a couple of important numbers to get right if you want it to work well. Not difficult though with other people's trial-and-error at your disposal.
http://algaescrubber.net/GuideThumb.jpg . . . . . The Super Guide to Algae Turf Scrubbers Part 1
algaescrubber.net
Also, i did read or skim all of this thread and i probably just missed it but i don't remember how you were measuring phosphate. Phosphate is notoriously hard to measure and i found out the hard way. Do yourself a favor and get a hanna checker. no color guessing... it passes light through your water sample and gives you a digital number. They are the most reliable for phosphate, especially when you get to low range. Anyway im not by any means an accomplished SPS keeper but that was my experience of the point that kind of tipped the scales in my favor. Just a thought. My SPS are all growing, certainly not as colorful as they could be but i am in the process of tuning the new ATS i built for my upgrade this year. I suppose any other method people are successful at is of course a valid choice too. I just personally like letting nature do the work. Less chance of something drastic happening.
