Calcium is creeping up despite not dosing.

[Bassett22]

Ive got a 250 gallon system, I have kalk stirrer that I run my ATO through that adds about 5-7 gallons through evap ever 3-5 days. I also dose 150ml a day to keep my alk at 200ppm, I was dosing 75-100 ml a day of calcium to keep it around 420-450, but my calcium started to creep up, one week, it was at 500, so I cut my dose in half, couple days later it was 540, so I stopped dosing completely, tested last night and its 600? :squigglemouth: What do I need to check? Where is this calcium coming from? Is it possible for a tank to stop using calcium for some reason and the kalk is still adding it? What do I need to test and figure out what is going on? I use BRS cal alk and mag, dosed as they recommend.

 

[badfinger]

Stop using the kalk

 

[evolved]

Where is this calcium coming from?

From the kalk you're dosing. That does more than just contribute to alk; you are effectively still dosing calcium.

I would be surprised if your Alk is not creeping up as well.

Use far less kalk, or stop using it entirely.

 

[JimWelsh]

When Do Calcium and Alkalinity Demand Not Exactly Balance? by Randy Holmes-Farley - Reefkeeping.com

 

[Randy Holmes-Farley]

Long term of of limewater (kalkwasser) tends to raise calcium. It does in my tank. So don't combine it with a high calcium salt mix.

The reason is detailed here:

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.

 

[Bassett22]

From the kalk you're dosing. That does more than just contribute to alk; you are effectively still dosing calcium.

I would be surprised if your Alk is not creeping up as well.

Use far less kalk, or stop using it entirely.

Kalk alone does not keep up with the demand of my tank. I was running it exclusively for a whole but my demand grew to the point that more dosing was needed. Rather then shut down the kalk and only dose. I decided to allow kalk to provide what it can and save a little by dosing the difference. If i stop kalk, i will go from dosing 100 ml a day to way more.

 

[Bassett22]

Long term of of limewater (kalkwasser) tends to raise calcium. It does in my tank. So don't combine it with a high calcium salt mix.

The reason is detailed here:

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.

Kalk alone doesn't meet the demand of my tank, ive started 2 part dosing as a way to keep the two in balance. Dosing calcium was fine for a while, but without any drastic changes to live stock. Calcium has suddenly not been used as quick as it was in the past.

 

[Randy Holmes-Farley]

Kalk alone doesn't meet the demand of my tank, ive started 2 part dosing as a way to keep the two in balance. Dosing calcium was fine for a while, but without any drastic changes to live stock. Calcium has suddenly not been used as quick as it was in the past.

Unbalanced apparent demand between calcium and alkalinity is usually caused by water changes with a salt mix that doesn't match the tank, but if the two parts of the two part system are not exactly themselves balanced, then that might also cause apparent imbalances in demand when it is in reality the additive.