Alk dropping?

[Kenmx10]

I have a frag system that I set up 3 months ago that is about 70 gallons total. It has 40 lbs of dry Pukani that is cured now, that has zero coraline algae. I added 2 rocks to seed the coraline, about 1o lbs. I've been dosing 16 oz of Kalk daily (two teaspoon/gallon ratio) . At this ratio, my calcium stays at 420, but my Alk drops about .9 DKH per day.

I have no corals in the tank yet. So Im wondering why the alkalinity is drooping that much faster than the calcium?

 

[Kenmx10]

dropping

 

[Randy Holmes-Farley Verified Community Expert]

The calcium probably is dropping too, but you don't notice it against the water changes. For a 0.9 dKH alkalinity drop, calcium will drop by no more than about 6 ppm per day, and our test kits cannot generally see that over a short period.

If you can, I'd up the limewater (kalk) dosing to match the alkalinity demand, or if you cannot due to evaporation rates or excessively high pH, I'd use some two part in addition so that alk is leveled off where you want it.