Kalkwasser saturation mixing time experiment

[rishma]

TLDR - it took 40 minutes of vigorous mixing to reach a 99% saturated kalkwasser solution.

Experiment
12L of ~20C RODI was mixed with 25g of kalkwasser to create a saturated solution. Saturation was measuring using a conductivity meter. The solution was mixed with a power head which strongly circulated the small container. Surface agitation was minimal.

Conductivity measurements were logged every 2 minutes. The datapoint at 30 minutes was missed because the meter timed out and turned off. I stopped the experiment at 60 minutes and 99.4% saturated because my battery was dying and my attention span was exceeded.

Saturation conductivity was determined by mixing 2 tablespoons of kalkwasser in 200ml of RODI at 20C.

I assumed that percent saturated was linearly proportional to conductivity. @Randy Holmes-Farley please confirm this is reasonable.

Results

Conclusion
For 30 years I have not been mixing my kalkwasser solution long enough to saturate. The solution is ~96% saturated after 10 minutes, which is still pretty good.

 

[Randy Holmes-Farley]

Thanks for the experiment!

 

[Fish Fan]

You're really getting your money's worth out of that conductivity meter I see

Nice work!

 

[Useful_Idiot]

Interesting! I wonder if the solution would get to full saturation from the 96 after some amount of time? Or if it needs agitation to get there.

 

[rishma]

Interesting! I wonder if the solution would get to full saturation from the 96 after some amount of time? Or if it needs agitation to get there.

Good thought. I doubt it increases much more without agitation, but I’ll measure again tomorrow to see if it went up or down from 99.4%.

 

[EnterName]

Very interesting, thank you!

Any info on how pure the used calcium oxide or calcium hydroxide was? The actual saturation might be even lower when the used reagents contained impurities, which dissolve fast and increase conductivity.

I rarely use Kalkwasser, but tend to use freshly made RO/DI which is colder. I wonder if this speeds up the process as calcium hydroxide's solubility is slightly increased in cold water.

 

[rishma]

Very interesting, thank you!

Any info on how pure the used calcium oxide or calcium hydroxide was? The actual saturation might be even lower when the used reagents contained impurities, which dissolve fast and increase conductivity.

I rarely use Kalkwasser, but tend to use freshly made RO/DI which is colder. I wonder if this speeds up the process as calcium hydroxide's solubility is slightly increased in cold water.

It’s BRS pharma grade kalkwasser, whatever that means.

Certainly saturation increases with lower temp but I am unsure if speed would change much.

 

[Thrillik]

If you mix a big batch of Kalkwasser and slowly use it over a month, will saturation deteriorate over time? If so, would re-mixing cause it to re-saturate?

 

[rishma]

If you mix a big batch of Kalkwasser and slowly use it over a month, will saturation deteriorate over time? If so, would re-mixing cause it to re-saturate?

@Randy Holmes-Farley wrote and article years ago that showed it did not lose potency over time in a closed (not sealed) container.

http://reefkeeping.com/issues/2003-05/rhf/feature/index.htm

 

[Boehmtown]

If you mix a big batch of Kalkwasser and slowly use it over a month, will saturation deteriorate over time? If so, would re-mixing cause it to re-saturate?

It does not fall out of solution. But I don't know if you put enough powder to saturate 3 times the water volume if you can refill the bucket and mix 3 times without losing potency being in the water.

 

[Thrillik]

It does not fall out of solution. But I don't know if you put enough powder to saturate 3 times the water volume if you can refill the bucket and mix 3 times without losing potency being in the water.

Also an interesting question and, selfishly, relevant to my situation with a 44g brute can.

Really appreciate all of the research here!

 

[Thrillik]

What happens if you continue to mix it after full saturation? Anything of note? What if the kalkwasser was always being mixed?

 

[rishma]

What happens if you continue to mix it after full saturation? Anything of note? What if the kalkwasser was always being mixed?

If the the container is totally sealed, you can keep mixing it and nothing else happens. In an open container, aeration from mixing will eventually introduce enough CO2 to start reducing the potency as calcium carbonate is formed.

 

[IPT]

It does not fall out of solution. But I don't know if you put enough powder to saturate 3 times the water volume if you can refill the bucket and mix 3 times without losing potency being in the water.

I'd be curious about this. Also what effect, if any it has when stirring up the remaining contents on the bottom of a container. I often wonder if I even need to add more fresh Kalk or if I could just stir up what's settled on the bottom for a while.

 

[Thrillik]

If the the container is totally sealed, you can keep mixing it and nothing else happens. In an open container, aeration from mixing will eventually introduce enough CO2 to start reducing the potency as calcium carbonate is formed.

And would this reduction in potency be measurable via a conductivity probe?

What probe are you using?

 

[rishma]

And would this reduction in potency be measurable via a conductivity probe?

What probe are you using?

Yes it would be measurable. The calcium carbonate precipitate would pull the Ca and OH out of solution.

I am using a Thermo Scientific Orion Star A222 with a DuraProbe 4-cell

 

[rishma]

I'd be curious about this. Also what effect, if any it has when stirring up the remaining contents on the bottom of a container. I often wonder if I even need to add more fresh Kalk or if I could just stir up what's settled on the bottom for a while.

You could remix and make a fresh solution with excess kalk powder in the bottom. Some portion of the sediment would be impurities and calcium carbonate and wouldn’t dissolve.

 

[Thrillik]

Yes it would be measurable. The calcium carbonate precipitate would pull the Ca and OH out of solution.

I am using a Thermo Scientific Orion Star A222 with a DuraProbe 4-cell

Thanks for all of the info! Re-mixing the kalkwasser batch I made yesterday that I only mixed for a few minutes.

 

[Randy Holmes-Farley]

If you mix a big batch of Kalkwasser and slowly use it over a month, will saturation deteriorate over time? If so, would re-mixing cause it to re-saturate?

Not to any concerning degree if you keep it closed and unstirred, such as in a Brute trash can.

 

[Randy Holmes-Farley]

You could remix and make a fresh solution with excess kalk powder in the bottom. Some portion of the sediment would be impurities and calcium carbonate and wouldn’t dissolve.

That’s what I always did.