how concentrated is my kalkwasser?

[salty joe]

I read that saturated calcium hydroxide has a pH of 12.4. The pH of the kalkwasser coming out of my kalk stirrer is 12.15.

Can I get a ballpark of how close that is to saturated from that info?

 

[Reeferdood]

I read that saturated calcium hydroxide has a pH of 12.4. The pH of the kalkwasser coming out of my kalk stirrer is 12.15.

Can I get a ballpark of how close that is to saturated from that info?

@Randy Holmes-Farley

 

[Randy Holmes-Farley Verified Community Expert]

About half potency, if accurate. For a better test without a conductivity meter (the best method), make some truly saturated limewater (2 tablespoons in a cup of ro/di ) and compare your pH to it. A difference of 0.3 pH units is about a factor of 2.

 

[salty joe]

Thanks, I'll do that.
The RO/DI water that feeds the kalk stirrer has a loose dust cover. Do you the think feed water could take on enough CO2 to make much difference?

 

[Randy Holmes-Farley Verified Community Expert]

Thanks, I'll do that.
The RO/DI water that feeds the kalk stirrer has a loose dust cover. Do you the think feed water could take on enough CO2 to make much difference?

Normal ro/di will take in CO2 far more slowly than actual limewater, and most folks just have a loose cover on it (I used a brute trash can). Just be sure to not stir it after mixing is done as that hastens entry of CO2 and degradation of the limewater.

 

[salty joe]

Could a refractometer be used to gauge the concentration of kalkwasser?

 

[Randy Holmes-Farley Verified Community Expert]

Could a refractometer be used to gauge the concentration of kalkwasser?

Not a hobby one, no. Wrong range and insufficient precision.

 

[Rst]

Randy, are you recommending only stirring Kalkwaser when making a new batch and thereafter not re-stirring until you make the next batch? I always thought Kalkwaser was best and maximized its potency longer if stirring is continuous during dispensing.

 

[Rst]

Randy, I always assumed kalkwaster retained its potency longer if continuously stirred during dosing. Is this wrong?

Sorry I thought my post didn’t get posted. Please delete double post.

 

[Randy Holmes-Farley Verified Community Expert]

Randy, are you recommending only stirring Kalkwaser when making a new batch and thereafter not re-stirring until you make the next batch? I always thought Kalkwaser was best and maximized its potency longer if stirring is continuous during dispensing.

For delivery from a large reservoir (my preferred method), stirring after initial mixing only serves to drive in CO2, depleting it. I prefer to let it settle, and dosed for a month or more from it. It does not go bad sitting if covered.

If you use a "stirrer" where you continually add new water, then you will need to frequently stir and work hard to keep out CO2.

I show data on a settled reservoir here:

The Degradation of Limewater in Air - Reefkeeping.com
http://reefkeeping.com/issues/2003-05/rhf/feature/index.htm

 

[dimidragos]

Hello, i have also a Deltec KM500 kalkwaser mixer ready to use but honestly i still don't understand how ....
I plan to use a peri pump from the ATO reservoir to the mixer then to the sump.
I don't know how much kalkwasser to add first time and when to replace the kalkwasser or when to add new....
According with some calculation i must add 1.6 liter of saturated KW to maintain alk.
I will appreciate any help

 

[salty joe]

The stirrer holds a surplus of kalk with the idea of keeping the kalkwasser within saturated. I'd try to find directions for that stirrer, but generally they hold two or three inches of kalk. Replace the kalk when it gets depleted.
How much kalkwasser you can add has as much to do with the display tank as it does the stirrer. Obviously, you can only add as much kalkwasser as is evaporated from system. You might want to start off slowly, adding less kalkwaser than you've calculated. Keep a close eye on alk.
I can't meet my tank's demand with kalkwasser because I don't evaporate much water. But it's a good start and helps solve my low pH problem.

If I had the room, I'd use a Brute trashcan filled with kalkwasser because it's simpler. My preferred method too.

 

[TexasTodd]

Hi Randy, I thought I had read the max water would hold (varies with temp) was like two tablespoons per gallon. It must be able to take more if you're saying to use 2 tbs per cup. ??

 

[YankeeTankee]

Normal ro/di will take in CO2 far more slowly than actual limewater, and most folks just have a loose cover on it (I used a brute trash can). Just be sure to not stir it after mixing is done as that hastens entry of CO2 and degradation of the limewater.

Nice article on degradation Randy. Is it really as simple as adding kalk to a 55g brute, mix it for a few min, then cover it with a loose lid and dose via peristaltic pump? But doesnt it fall out of solution to the bottom after days of no mixing?

 

[LadyTang2]

There's an older article on R2R that I'll paraphrase a bit "Calcium hydroxide powder isn’t soluble in water, it won’t dissolve. The powder remains either suspended in the water column or settles out at the bottom. Left to settle at the bottom, calcium hydroxide is rather useless for buffering ph and it needs to be consistently mixed with freshwater to remain useful."
Randy you do use the word dissolve and I see it elsewhere, is this article incorrect? Is also incorrect about the need for mixing often? I think this is what yankee is talking about, it settling out at bottom after no mixing.

 

[YankeeTankee]

There's an older article on R2R that I'll paraphrase a bit "Calcium hydroxide powder isn’t soluble in water, it won’t dissolve. The powder remains either suspended in the water column or settles out at the bottom. Left to settle at the bottom, calcium hydroxide is rather useless for buffering ph and it needs to be consistently mixed with freshwater to remain useful."
Randy you do use the word dissolve and I see it elsewhere, is this article incorrect? Is also incorrect about the need for mixing often? I think this is what yankee is talking about, it settling out at bottom after no mixing.

So you're wondering if the proper term is suspended or dissolved (as this article says kalk does not dissovle).

That's interesting but either way, can we simply poor 40g rodi in a container w 2tsp/gal kalk and leave it there unstirred for weeks without it settling to the bottom (no longer suspended or dissolved?)

 

[DeputyDog95]

About half potency, if accurate. For a better test without a conductivity meter (the best method), make some truly saturated limewater (2 tablespoons in a cup of ro/di ) and compare your pH to it. A difference of 0.3 pH units is about a factor of 2.

Why do you prefer the conductivity meter over a pH meter? Just curious.

 

[Randy Holmes-Farley Verified Community Expert]

pH is much cruder since it is a logarithmic scale ( a 0.3 pH unit difference is a doubling of potency) and a meter calibrated at pH 7 and 10 will not be especially accurate at pH 12.5.

Potency is linear with conductivity, and is easily read at 5-10 mS/cm (50-100% potency) with an appropriate meter.

 

[Randy Holmes-Farley Verified Community Expert]

So you're wondering if the proper term is suspended or dissolved (as this article says kalk does not dissovle).

That's interesting but either way, can we simply poor 40g rodi in a container w 2tsp/gal kalk and leave it there unstirred for weeks without it settling to the bottom (no longer suspended or dissolved?)

I know that post is very old, but calcium hydroxide certainly dissolves in pure water. If there are also extra solids beyond what dissolved, then that is termed a slurry.

 

[Randy Holmes-Farley Verified Community Expert]

There's an older article on R2R that I'll paraphrase a bit "Calcium hydroxide powder isn’t soluble in water, it won’t dissolve. The powder remains either suspended in the water column or settles out at the bottom. Left to settle at the bottom, calcium hydroxide is rather useless for buffering ph and it needs to be consistently mixed with freshwater to remain useful."
Randy you do use the word dissolve and I see it elsewhere, is this article incorrect? Is also incorrect about the need for mixing often? I think this is what yankee is talking about, it settling out at bottom after no mixing.

I do not know which article says that, but if it does literally say that, it is wrong.