Calcium decreases as Alk Increases? Can't maintain a stable Ca value

[ReeferDog]

On 10/31/24, I set up a daily AWC system with (2) Versa's, changing out about 10L per day. I am mixing my saltwater to salinity of 1.024-1.026 using Instant Ocean (regular mix). Initially, I saw a slow increase in Ca values that crept above 550, and with some intermediate water changes and reduction to daily Ca dosing, I was able to get Ca to a normal range. Now the Ca value keeps dropping, no matter what increase I make to the Ca solution daily dose. I have a Kalk stirrer that runs 24hrs/day with the same dose I've used for a year, although I did recently change brands of Kalkwasser powder from Avast Marine to BRS (temporarily).

I saw some articles from RHF about interdependance of Alk and Ca, and wanted some advice. Is increasing Calcium as simple as increasing daily dose to get it back in range and then maintain that dose?

Display Tank is 150g, frag tank is 40g, and sumps hold another 60 gallons, for 250g total volume. Mixed reef, heavy SPS, which are encrusting, growing, and have great PE.

 

[Randy Holmes-Farley Verified Community Expert]

Kalk cannot correct low calcium. It actually slowly drives calcium higher when maintaining alk.

What are the current calcium and alk values?

 

[Miami Reef]

Is increasing Calcium as simple as increasing daily dose to get it back in range and then maintain that dose?

Very close. You first need to raise the calcium individually with calcium chloride, then you can maintain it with kalkwasser.

Kalkwasser a little calcium heavy, but that’s besides the point.

What’s the calcium reading?

 

[ReeferDog]

Alk is 8.4 and stable, Ca is 311, down from 375 early last week.

 

[ReeferDog]

Those are readings from my Trident as of right now. I did perform a Trident calibration on the until about 4-5 weeks ago, but will probably do another calibration tonight, just to be sure its up to date.

 

[Randy Holmes-Farley Verified Community Expert]

Calcium didn't decline that much with alk stable. I expect a trident error. It seems especially problematic when reagents begin to get low.

 

[ReeferDog]

Thanks Randy and MiamiReef. I did have to replace A and B reagents in the last 2 weeks. I will calibrate the Trident tonight and if I have a manual test kit, I'll verify the new Trident readings cross referenced with a manual test.