And check to see that your phosphates are ZERO as they are a major contributor to hair algae in my experience.
Best way to help remove/reduce phosphates is to:
1. Use RO or better yet RO/DI water for all make-up water and water changes
2. Drip Kalk if you are not already doing so. Kalk precipitates phosphates immediately on contact and has the added benefit of maintaining your calcium levels.
3. Keep a refugium with caulerpa (sounds like you're already doing so)
4. Keep up the manual pruning of the stuff.
It was a plague in my tank about a year ago and took over 6 months to tackle, but did eventually completely dissapear. Just another one of those "natural cycles" in a marine aquarium I think.
I've lived through both hair algae and Aiptasia, I can live through anything now! (Including the nasty red-slime algae that has decided to now pop-up the past month) And here my tank was so nuisance free for so long!!! Sigh.
