Kalkwasser reactor and a pH probe

[Sinekal]

Hi All,

I am upgrading from a reef keeper to an apex, and am focusing on how it can make my set up safer, and save me time and effort. Once my system became stable my goal has been increased safety and redundancy, along with the simplification or reduction of maintenance requirements. To that end I was thinking I could use the extra pH probe I now have to use my kalk more efficiently. Today I dose kalk through a reactor and change out the kalk on a set frequency. I know it isn't exhausted, but consistent alk is important to me, so I simply change it more frequently than required. I know pH is not a perfect measure that lime water is full saturated, but I am under the impression the pH will fall when its no longer saturated, and could be used to indicate its time to change the kalk. Is anyone doing this currently? Where did you place the probe? At what pH do you change out your kalk?

I am aware the conductivity is a better measure to saturated limewater, but that is a very expensive upgrade, and at this time I am just trying to determine if I can use the equipment I have to improve my current methods.

Thanks for looking and I greatly appreciate your thoughts and advice.

[Sinekal]

Bump

[ca1ore]

You may be overthinking things. A pH probe can be useful in controlling a calcium reactor, but I'd not bother with trying to monitor Kalk. Just add fresh power every couple of weeks and clean the entire thing out every couple of months.

[Sinekal]

That's what I'm trying to determine, is it even worth trying, or just a thought. Thanks for the reply.

[Randy Holmes-Farley]

It may not be worth the trouble. The pH will vary considerably with the temperature, and a drop of less than 0.3 units will be a loss of 50% of the dissolved calcium and hydroxide. At saturation, the pH is 12.54 at 25 ºC, 12.627 at 20 ºC and 13.00 at 10 ºC, 12.289 at 30 ºC; 11.984 at 40 ºC. So if the temp changes, it might convince you the water is OK, or undersaturated, when it reality it may not be.

More precise would be to measure it by conductivity. I do that every time I mix limewater. Saturation is about 10.3 mS/cm, depending on the temperature.

[Sinekal]

Thanks for the explanation Randy. That helps a lot.

[Randy Holmes-Farley]

You're welcome.

Happy reefing.

[onecansay]

Originally Posted by Randy Holmes-Farley

It may not be worth the trouble. The pH will vary considerably with the temperature, and a drop of less than 0.3 units will be a loss of 50% of the dissolved calcium and hydroxide. At saturation, the pH is 12.54 at 25 ºC, 12.627 at 20 ºC and 13.00 at 10 ºC, 12.289 at 30 ºC; 11.984 at 40 ºC. So if the temp changes, it might convince you the water is OK, or undersaturated, when it reality it may not be.

More precise would be to measure it by conductivity. I do that every time I mix limewater. Saturation is about 10.3 mS/cm, depending on the temperature.

Hello Randy. Do you have one of your articles to point me at to explain the Kalk/conductivity relationship.

Thanks

[Randy Holmes-Farley]

I think I discuss it here:

What Your Grandmother Never Told You About Lime
http://reefkeeping.com/issues/2005-01/rhf/index.htm

The conductivity is mostly linear with concentration.

from it:

Limewater that is saturated with calcium hydroxide has a pH of 12.54 at 25ºC. It is actually recognized as a secondary pH standard. The pH is substantially higher at lower temperature (12.627 at 20ºC and 13.00 at 10ºC), and lower at higher temperature (12.289 at 30ºC; 11.984 at 40ºC). Saturated limewater has a conductivity of about 10.3 mS/cm at 25ºC, and contains about 808 ppm of calcium and 40.8 meq/l of alkalinity. Slightly more calcium and alkalinity dissolve at lower temperatures, and less at higher temperatures. Of interest to chemists, a large fraction of the calcium in saturated limewater is present as the ion CaOH+, with the remainder being Ca++. The CaOH+ will instantly dissociate into Ca++ and OH- upon its addition to aquarium water.