Reducing nutrients -> kH / ca relation

[Aquamechanic]

I started using Rowa Phos GFO about a year ago on my tanks. Has worked very well to reduce PO4 to 0.1 - 0.03.
NO3 <10

Since the levels of PO4 have dropped it seems I am having a harder time keeping kH and Ca in check. Both seem to want to drift down at a much higher rate.

Corals look better overall so it just may be that they are consuming more but the difference is huge with Alk

Thoughts?

 

[Bent]

Supposedly GFO will lower alkalinity. I experienced this as well. Before I ran any GFO my dkh was about 9. After I installed the reactor it went to about 6-7. I had to start using a kalk reactor to pull it back up.

Now whether or not this is because of the GFO itself, or the lower P content, I'm not sure. Though with my limited chemistry knowledge, I don't think that P will affect alkalinity.