Kalk and pH in top-off

[BigDave]

Hi All,

I had a second pH probe, so I tossed it into my top-off tank that I add Kalk to.

I've done some research and I've noticed that pH jumps to 12 or so when fully saturated and the water has settled after first adding.

The pH slowly drops down as the water level drops in the ATO and over time. The odd thing is, I can tell when the ATO is almost empty because the pH in it starts to drop rapidly.

This leads me to some questions as I'm trying to understand what's going on. I also want to build a kalk reactor and I'm trying to use this knowledge in the design.

So, my questions are.

I'm assuming this means the amount of kalk saturated in the upper levels of the ATO water is less than near the bottom?

Is it better to pull the water in near the top levels of the tank?

Should I be measuring the pH of the upper water? Right now I have the probe pretty much sitting on the bottom of the ATO tank.

The kalk reactor I want to make will use a paddle stirrer and the water will exit near the top... similar to the Avast one. The pH probe will be mounted at the top of the reactor.

I guess the real question I've run in to... how does the reactor operate differently then just adding the Kalk to the top-off. Does it just allow much more kalk to be added to the water keeping it in a super-saturated state instead of adding it more often?

[bertoni]

The Kalk concentration will be the same throughout the mix if the water is stirred even a minimal amount. Is this reservoir getting any stirring? I'm not sure what's happening. If the pH actually is dropping, then the Kalkwaser could be getting carbon dioxide in it, and thus the Kalk would be converted to calcium carbonate. I might try rinsing the probe carefully along the way, and checking the calibration. pH measurement problems are fairly common, and Kalkwasser is a fairly challenging environment.

[BigDave]

The container is a 10 gallon tank with a lid, but isn't sealed.

The only stirring it may get is when the top-off pump is turned off and the water rushes back out of the hose.

The pH probe sits on the bottom of the tank. I'm wondering if it's too close to the stuff on the bottom.

I'll try to find a way of suspending it this weekend to keep it higher up. I'll also stick some type of elbow on the pump to make sure it's pulling clearer water. I think it's sometimes pulling some of the stuff on the bottom because I can see little pH spikes in the main tank each time the top-off runs.

[bertoni]

There's some chance that the bit of flow is causing the degradation of the lime. That's my first guess, if the pH meter is reasonably stable in its reading.