pH probe to read saturated limewater

[BigOC]

I have a pH probe in a DIY kalk reactor. I know it is not the ideal way of measuring saturation, but the probe reads 11.9 when I believe it is fully saturated (added 2 tsps in less than half a gallon of RODI water). Within a few hours the pH probe measures drop from 11.9 to 11.4. This drop happens without doing anyting to the limewater (nothing added or removed). Is that normal? I do dose some kalk overnight but jsut a few milliliters so technically it should drop as days go by, but the weird part is that the measurements move up and down in a range from 11.2 to 11.7. Is the probe bad? I was using it recently in the tank and the measures were very steady around 8.2

 

[Randy Holmes-Farley]

pH is a very crude way to read potency, but it can be used.

Your values are likely well off, or it is VERY weak. The pH of saturated limewater (kalkwasser) is about 12.54 at 25 deg C and each drop of 0.3 pH units is a drop of 50% in potency. If real, you values indicate 23% and 7% of saturation.

Conductivity is the best way to gauge potency, but for using pH, determine the pH in a truly saturated limewater solution (say, 2 tablespoons dry solid calcium hydroxide or oxide in a cup of RO/DI). Whatever it is, record it.

Then compare the solution you are interested in that value to get a rough estimate of potency.

 

[BigOC]

pH is a very crude way to read potency, but it can be used.

Your values are likely well off, or it is VERY weak. The pH of saturated limewater (kalkwasser) is about 12.54 at 25 deg C and each drop of 0.3 pH units is a drop of 50% in potency. If real, you values indicate 23% and 7% of saturation.

Conductivity is the best way to gauge potency, but for using pH, determine the pH in a truly saturated limewater solution (say, 2 tablespoons dry solid calcium hydroxide or oxide in a cup of RO/DI). Whatever it is, record it.

Then compare the solution you are interested in that value to get a rough estimate of potency.

Thanks Randy.

I have tried a couple of things and I cannot get it to a point that makes sense yet.

I added 2 tbsp of kalk to a cup of RODI and the pH probe was still giving me 11.9, so I assume it's not working well or needs to be calibrated. I did measure the pH on that saturated solution with a different ph tester and it measured 12.8. So I need to calibrate / replace the nepture pH probe, but I re-calibrating with the normal process (4 and 7 reference fluids) is not helping me, is there a different way I can calibrate it to operate at higher values? The other point that confuses me is the fact that the pH reading with the Nepture probe goes down in just a few hours without doing anything.

The kalk reactor measured 12.8 with the other tester as well, so I assume the potency is still ok ...