Kalkwasser - high calcium, low alk

pomoev · May 31, 2022

Hi.

I switched from 2-part to Kalk in January and since then my Calcium has been above the proper levels. My salt is RedSea blue bucket (Ca - 420-440ppm). For the last month, I've been dosing 30ml of saturated kalkwasser from a stirrer every hour, 720ml a day. Water volume is ~100g. Today I did the tests and my Ca is at 450 while Alk is at 6.4 dKH. From what I read Kalk is supposed to supply Ca and Alk in the right proportions. Why is my Ca growing and Alk decreasing? The pH is usually around 7.8 at night and about 8 during the day.
Should I just dose Alk separately in addition to Kalk? Are there other recipes?

Thank you.

The Farmer · May 31, 2022

I have a similar setup, I dosed ALK until I was able to stabilize ALK and calcium while using kalk

Garf · May 31, 2022

pomoev said:
Hi.

I switched from 2-part to Kalk in January and since then my Calcium has been above the proper levels. My salt is RedSea blue bucket (Ca - 420-440ppm). For the last month, I've been dosing 30ml of saturated kalkwasser from a stirrer every hour, 720ml a day. Water volume is ~100g. Today I did the tests and my Ca is at 450 while Alk is at 6.4 dKH. From what I read Kalk is supposed to supply Ca and Alk in the right proportions. Why is my Ca growing and Alk decreasing? The pH is usually around 7.8 at night and about 8 during the day.
Should I just dose Alk separately in addition to Kalk? Are there other recipes?

Thank you.

Calcium does rise slightly with kalk and is largely corrected through water changes if that salt has a lower calcium level. Calcium at 450 is no problem as far as I can tell but you could always just dose baked sodium bicarbonate for a while if you wanted, till the calcium comes down further.

Edit - I’d just increase your Alk a bit unless your running it that low for a reason.

Randy Holmes-Farley · May 31, 2022

I agree. Limewater/ Kalkwasser is slightly overbalanced to excess calcium.

Here's my comment from a previous article:

Calcium (Ca). In my reef aquarium, I use only Instant Ocean salt and I have not added any additional calcium except as limewater for a number of years (during which time I have continued regular 1% daily water changes). So why is my calcium level (472 mg/L) higher than one would normally expect for Instant Ocean (maybe between 350 and 400 mg/L)? That long term rise in calcium is actually the expected result when using limewater to maintain alkalinity.

Limewater adds calcium and alkalinity in exactly the same proportions as in pure calcium carbonate. So if that is what is used by corals to make skeletons, and what precipitates on pumps and such, then calcium would stay constant.

But both magnesium and strontium get into growing calcium carbonate crystals in place of some of the calcium. A few percent of the calcium is replaced this way. Consequently, since the same amount of alkalinity (the carbonate) is used over time, and somewhat less than the balancing amount of calcium, calcium rises if alkalinity is maintained. I’m happy to see the result match the theory, and the calcium level seems fine to me.

Nano sapiens · May 31, 2022

I also use the RS Blue Bucket and Kalkwasser. When my reef aquarium calcium levels reach ~460 I reduce my Kalkwasser dosing amount slightly (to create a calcium deficit) and add an alkalinity boosting product (Seachem Reef Builder) to keep alkalinity stable. I keep this up until calcium is back down to ~410 and then I resume my normal Kalkwasser dosing.

I have been doing this for years. IMO, a minor inconvenience considering the overall beneficial effects of using Kalkwasser.