Good Alk, Ca, LOW pH!!

[BPiers]

I run a calcium reactor on a heavily stocked SPS 93 gal reef.
All top off water is Kalkwasser

pH is low (even lower than I thought after calibrating my 3 apex Lab probes.) Was 7.6, now reads 7.48.
Alk is 9.3 solid, Ca 446 (Hanna checkers).
Is it possible my probes/config is off? or is the pH that low with the Alk levels that high? I have a CO2 scrubber on my skimmer.

I can add Alkalinity, Kalk, whatever. The pH rises but drops back down within an hour. How is this possible?

I've done a collective 55 gallon water change over the past few days.
Everything in the tank is looking great, I'm just concerned with the low pH readings.

 

[anthonywesty]

PH 7.48 could be a bad reading due a bad probes or bad calibration fluid.

 

[Bob Escher]

After reading this issue over different forums and recalibration get my PH probes numerous times I went out and bought a Hanna PH checker. After calibrating it in fresh water ( RO/DI) saltwater and my tanks water it told me a different story. My probes I calibrated the same way with fresh, salt, but first was calibration fluid for all of them ( 4.0 and 7.0)
I don't know what it is and no one has ever given I good explanation ( at least from I could understand why) but my checker was or is higher by .53 in other words my probes were at 7.67 and my checker always gives me a reading of 8.19 or 8.2