Calibrating apex conductivity probe for kalk stirrer

[Velcro]

Hi there,
I'm looking for help on how to calibrate the probe for this application. Do I just use the standard 53,000 mS solution to calibrate it? I have tried using this and can't get past 8.3 mS on freshly prepared saturated kalkwasser (2+ tsp in like 1 cup of water...).

 

[Velcro]

I looks like the closest calibration point available on the apex is 6668 µS/cm. I have some KCL monohydrate, do you know what concentration I would need to make this reference solution? I have a jewelers balance as well.

 

[Randy Holmes-Farley Verified Community Expert]

I don't know the APEX, or how to adjust it (I know folks have issues with its conductivity measurement), but I also don't think exact calibration is needed.

If you determine that 8.3 mS/cm is the value you get for truly saturated limewater (say, 2 teaspoons in a cup of RO/DI stirred for a bit), then just use that to monitor the saturation (so 4.15 is about half saturated, etc.).

 

[Velcro]

@Randy Holmes-Farley

So as you have mentioned several times in the past, it appears that my kalk stirrer does not have saturated level at the higher levels of the unit. I refilled the reactor last night and calibrated my probe with a DIY 6668 microSiemens/cm solution (found the appropriate amount of KCl in some research papers). Upon initial calibration I made some fully saturated kalk solution in a 1L pitcher and washed my kalk reactor and refilled. Both the pitcher of saturated kalk and the newly filled reactor matched in conductivity, though the number is nowhere near the cited 10.3 conductivity that you have stated in the past. I'm guessing my conductivitiy probe is just old, but I'll just use 6.15 mS as my saturated level since it matched both my solutions.

As you can see from my log, the solution is becoming more and more dilute as the RODI is being run through it. I'm HOPING that it will eventually reach some sort of equilibrium and the drop in concentration will slow. If it slows down dropping considerably then I will be able to still use this method, but if it continues to drop like it has since last night I might go a different route than this stirrer. As it stands, I have to clean the reactor and fill with like a months worth of kalk to get a good week of holding my alk stable.

My goal of using the stirrer was to have limited weekly maintenance (just add kalk once a week and clean it out every 3-4 weeks). I wonder if the pump driven reactors would be better for keeping the solution saturated? My assumption is that the density of the kalk solution kinda stratifies so the newer water is inadequately mixing with the saturated water. Seems like a pump driven reactor would do a much better job of getting rid of this stratification.

Otherwise maybe I'll just figure out a way to have a large kalk only container in the room without looking awful. Keeping my ATO water mixed with kalk doesn't work for me because of variable evaporation due to use having windows open vs running AC on a day to day basis.

 

[rck329]

Velcro, I was thinking of doing the same thing with a kalk reactor. Did you find that the conductivity eventually reached equilibrium?

 

[Velcro]

Velcro, I was thinking of doing the same thing with a kalk reactor. Did you find that the conductivity eventually reached equilibrium?

Nope. got rid of it and now use a bucket with a lid. It stays rock solid between fillings.

 

[rck329]

Rats. I was hoping this may be a way to go. I guess I'll stick with my 30 gal brute. Was hoping just to save some space in the fish room. Thanks for the update!

 

[Velcro]

Rats. I was hoping this may be a way to go. I guess I'll stick with my 30 gal brute. Was hoping just to save some space in the fish room. Thanks for the update!

I have a theory that the pump driven stirrers would more thoroughly mix it between use but don't have one to test it. I'm just going to put a 20 gallon aquarium in a decorative chest or something and hold my kalk in there

 

[rck329]

I have a theory that the pump driven stirrers would more thoroughly mix it between use but don't have one to test it. I'm just going to put a 20 gallon aquarium in a decorative chest or something and hold my kalk in there

Yeah, it's hard to argue with the simplicity and consistency of a single batch. I was hoping a reactor would be fairly straight forward but it just doesn't seem to be the case. And the last thing I need is another variable.

 

[YumaMan]

I am building my own kalk stirrer because I am very cheap. I plan to make it very ugly so that nobody will steal it. Here it is: a black rubber garbage can to serve as a reservoir, and a 18 rpm 0.7 watt AC synchronous motor from China (eBay @7), 20 inch length of 1/2 inch diameter pvc pipe for a shaft, and a 3-blade 60 mm plastic trolling motor ($6 plus shipping) to stir. My Digital Aquatics ReefKeeper Lite will activate the motor for 1 minute every hour. After 58 minutes the RKL will activate a dosing pump to deliver 16 ml of RODI w/ kalk, then turn off. I will experiment with this system to stabilize my DT at a target pH of 8.2 =/- 0.05. I plan to dose less water than evaporates, so that my ATO takes care of any evaporation that I need to replace. Any ideas if I am on track to succeed? Do I need to concern myself with the conductivity for saturation in the above setup?