Calcium depleted using kalkwasser?

[Dave-T]

I just noticed that my coralline seems to be receding, so did some testing and I think my calcium is depleted. I maintain calcium and alkalinity with kalkwasser. My alk is fine - it varies between 9 and 10. I tested calcium with 3 kits - Red Sea, Salifert, and Hanna. The Hanna result is fine, it says 440ppm. But Salifert says 300, and calcium didn't even register with the Red Sea. The last ICP I did (Oceamo ICP-MS) was two months ago, and it said 498.

So I have questions!

Is Hanna calcium untrustworthy? Should I go by the salifert/red sea results?

How normal is it that calcium would become depleted when using kalkwasser, but alkalinity is fine? I have an automated alk tester (GHL KH Director), but no automated calcium testing. I've always thought I didn't need to pay close attention to calcium when using kalk, if the alk is fine.

Why would my calcium drop so quickly, after being stable for so long? I do monthly ICP tests, and it's always been fine. (I missed last month because I was travelling).

I guess I should bring it back up with 2 part, and then bring my calcium reactor back online to maintain calcium. How quickly is it safe to raise my calcium.

Thanks!

 

[Randy Holmes-Farley]

My expectation from all you write is that calcium is fine to high, not low. Didn't register with Red Sea, likely means you reached no endpoint and it is higher than one syringe can measure.

Try the kits you have on some new salt water.

Calcium cannot become depleted using kalkwasser unless you are adding large amounts of alkalinity in other ways. In general, kalkwasser actually adds a bit of excess calcium relative to alk.