Bay Area Reefers

What do you have in your tank? How is you Phosphate level?

if your parameters are good...I would say sea hare. Otherwise...phosphates (like I had) and nitrates will make hair algae grow faster then you can handle.

If you search 'hair algae' the first thread has some great posts. Once you get nutrients down it will just fall off. I had it for six months of pulling it by hand, and it coming back thicker, until it all just vanished, over a month or so, as I siphoned out the weekly water change. I added a refugium to use up the NO3. Then I went through six months of red algae and it too fell away. Always something.

+1 . Also when you are trimming the hair algae, make sure you remove all strands that are astray. Otherwise, you are back to square one, but in another location.

I threw some phosban in a media bag (small tank) and some black foot snails and it took care of it.

sea hare (Best HA eater)
tuxedo urchin
lettuce nudibrac
abolone
hermits
foxface, tangs

This is my cleanup crew for HA. I also got a GFO reactor from Bulk reef supply. But I did do lots of manual removal. Brok the reef apart scrubbed each rock by hand with a brush OUTSIDE the tank rinsed the rock off in saltwater. Then put the reef back together. Once hte crew and the GFO was in place the HA was not able to make a come back.

I feel your pain...
Been having issue with hair algea for a while too...
I have tried the sea hare, hermits and urchin but they can only eat what it is in there and doesn't solve the root of the problem.
My experience with sea hare is that some love the algea and some don't even touch it. My tank is too small and I can't keep them alive for crap. They die within weeks. I guess the variance in PH or something is too high. I don't know.
Weird thing is that HA must be the one taking up the nutrients, 'cause I test phospates and nitrates and they come as undetectable, so between HA and chaeto, they consume it all, but for some reason they don't want to die off.
I went though a lot of big water changes lately to fix up some othe issue of low mag I was having, so there was not much nutrient in the water. Then I scrubbed the rocks. The big water changes did wonders for the HA, but some of my corals didn't like much. They didn't die or anything, but I saw some acros had some color loss, but they recovered back up after a while. I did like 3x 50% water changes within a week.
After that, my rocks had just very small patches of HA that stayed small for about 2 or 3 weeks and I notice they started to grow slowly again. So I guess the nutrients are coming back and they started growing again, even after I added the GFO. I don't have a reactor though. They are just in a mesh inside the sump. Maybe I need more flow through it.
Joe also said there has been some people that had results with high mag, but that would irritate your snail a bit I would think.
So, I would say attack your nutrients and you should solve your problem.
That's what I've been trying to do.

I too have some hair algae in my tank, only on a small portion of rock which didnt get much flow, my phosphate is at 0.5 and nitrate around 15ppm, but I ran some phosphate sponge and am currently on a vodka dosing regimen and it is helping alot, I also redirected some more flow over to that area and now am seeing a decline in hair algae, also my hippo tang is enjoying eating it.

lawnmower blennies are great little algae eaters, I had one awhile back, took out all my hair algae in a week and I passed him on to another reefer, none of the sea hare's I ever bought lasted more than 2 weeks before I found them dead on the sand bed, and they can wipe your tank out if undiscovered or behind rocks, just FYI.

if you have the ability to do daily dosing, I would suggest looking into vodka dosing, it is very cheap and highly effective at reducing NO3/PO4.

also, dosing kalkwasser near your skimmer input has a way of reducing nitrate and phosphate, do to some type of percipitation of the elements, I dont know too much on how exactly it works, but research and you shall find.

robert - eastbayreefer2010

Is vodka really effective?

Vodka is effective in bringing down PO4 and NO3, but on occasion IME hair algae can still survive in nutrient poor environments there are other factors such as bioload, quality of live rock nutrient impaction in the sand bed and the surface of the live rock etc.