Alkalinity and magroalgaes

[Phantom Phish]

I recently added macroalgaes to my system (C. racemosa and Chetomorpha, and a very small amount of Halimeda). They are growing very well. My problem is ever since I added them my alkalinity, which was pretty stable at 3.5 meq/l, has dropped and I'm having a hard time keeping it up. I have a Nilsen kalk reactor adding kalkwasser on a dosing pump, running 24/7. And still I'm having to added additional buffer/alkalinity (using Kent super dKH). Calcium is right at 410.

I didn't think macroalgaes consumed anything that would lower my alkalinity. Am I wrong on that? Or is the alkalinity drop completely unrelated to my adding the macroalgaes?:confused:

[bigsteeviestyle]

I believe the macroalgae that is to blame is the halimeda. Halimeda incorpotates calcium into its mass.

[Phantom Phish]

Yeah, I know what you mean about Halimeda being a big consumer of calcium. But I really have only about 3 to 4 inches total length of the Halimeda, and about two to three gallons each of the caulerpa and chaetomorpha. And the thing that confuses me is my calcium has stayed where its always been (around 410 ppm), its just the alkalinity that I'm having trouble with. If anything, I thought the macroalgaes would use up more dissolved CO2, which would raise my pH and alkalinity. But just the opposite has happened. Any ideas?