Those dosing Kalk--how do you keep Ca balanced?

Jonify · Jan 6, 2021

When dosing Kalk (as a formal dose, not in the ATO reservoir), you typically have Ca increases disproportionate to alkalinity (albeit very slowly) since kalk is not a truly balanced additive. How do successful SPS reefers overcome this? Are water changes enough? Do you mix saltwater with lower calcium (so 34 ppt with most mixes) and then dose up alkalinity/Mg? Do you alter the kalk solution? I'm not using kalk (anymore), but I'm considering jumping back in and dosing it very slowly overnight, mostly to help with the diurnal swing (don't have room for a fuge)--which is a pretty fantastic use of fully saturated kalk, if normal daylight alk and pH ranges are good. But also considering it to eek out a little more runway from my ATO (I have a 20G nano, and am not willing to hook my RO up to the ATO [really bad experience with that], so that's a no-go--trying to focus this on the specific Kalk question asked originally

jda · Jan 6, 2021

It has been a long time since I dosed kalk in a reef tank, but when I did, I also would supplement with baking soda here and there (carbonate). You dose the kalk to meet the need of the higher level element, in your case calcium, and then add in a bit of baking soda to raise the alk. Do not dose them at the same time. Do not dose them in the same container. It is ok if the alk falls slowly over a few days and then you drip in a mixture to raise it back up.

FWIW - no tank that I have ever owned used carbonate and calcium in balance. I have used calcium reactor with natural medial for the past few decades, I have to sure-up my tank every 3-4 months as something drifts. It is usually a small number, but it still drifts.

nereefpat · Jan 6, 2021

For me, limewater has replaced my alk and Ca in the correct ratio. Along with CaRX, this is supposed to be an advantage of those two methods over 2-part. You can adjust over time, of course, as needed. If Ca drifts up on you, it would have to become pretty high to cause any issues, so water changes should cover that. I don't change much water, a couple gallons a week on a 125+sump.

I would calculate kalk additions based on alk, not Ca. The Ca tests have less resolution, and Ca doesn't need to be as stable. Testing Ca monthly or so should be fine.

I don't have much SPS (slimer, caps, chalice, that sort of thing). I come to the SPS forum to learn, and only chime in on a few subjects.