I have actually seen three types of Caulerpa. THey look like vines with feathers...I think the grape type is classified as a caulerpa...and there is a type that has broad leaves to it. I think that Caulerpa is not a species as much as it is a genus.
Anyways...Do a test of the distilled water for phosphates and silicates if you can. Distilled water comes from a source at times tainted with those chemicals and I dont know if distilling gets rid of them at all. Any excess of either of these nutrients will cause algae to thrive. Nitrates will also do the same thing but there is only so much you can do there.(Fish waste, decaying food, etc. contribute...you know this already though).
I used some phosgaurd in my tank(you only use it for a short time and it says it doesnt leach anything back into the tank at all). It will reduce your phosphates and a little bit of the other two. This might help...dunno though.
How much water circulation is there in your tank? I am battling cyno, and right now it grows in areas where the water flow is not that great. I remove it by hand and my photo period is 8&3(8 hours of daylight with atinic and 3hours of just atinic by themselves-dawn and dusk simulated). I had 13 hours of total photo period and the algae did great.
It takes 3-4 times as long to grow out of control now. Even if its for a short period of time...try reducing your photo period. Do this gradually if you chose to do it. The tank inhabitants wont like it as much if you go cold turkey with the lights. Have you read Justins thread on cyno? Do a search for cyno(on this website) and you will see one of the best bits of advice Ive read on these boards regarding cyno.(His method does not involve using chemicals :joy: )
Take your time and I wish you the best of luck with your battle.
ps...maybe you should sell the stuff on e-bay. I see a lot of people do that....Just kidding(nothing wrong with it though)