Low pH with Kalk and CO2 scrubber

[JD28]

Having issues getting my pH up (7.38 at night, 7.75 during the day). Corals look good, but not really growing. Dose Kalk (in sealed ATO) and have a CO2 scrubber installed as well. Good surface water exchange, could be better though. 90 gallon tank

Any thoughts or suggestions?

 

[Randy Holmes-Farley Verified Community Expert]

Welcome to Reef2Reef!

I think it unlikely that pH 7.38 is accurate.

How are you measuring it and when did you last calibrate it (and how)?

 

[JD28]

Welcome to Reef2Reef!

I think it unlikely that pH 7.38 is accurate.

How are you measuring it and when did you last calibrate it (and how)?

Thanks!
I'm measuring it using an Apex. Probe is ~ a month old. Last calibrated 2-3 weeks ago (used new 7&10 solution). Had several phone calls with Apex, really helpful, but got a few different answers regarding if probe/unit is working correctly.

 

[bubbgee]

Thanks!
I'm measuring it using an Apex. Probe is ~ a month old. Last calibrated 2-3 weeks ago (used new 7&10 solution). Had several phone calls with Apex, really helpful, but got a few different answers regarding if probe/unit is working correctly.

I have been using the same apex probe for three years and now I'm thinking i need to replace it. I am in the same situation you are in.. 7.6 to 8.05 pH with kalk dosing and CO2 scrubber..

CO2 scrubber worked the first three weeks of use. I replaced it with new media and it stopped working. Kalk in ATO used to work too, now I just have high Alk but no pH boost.

I'm out of ideas. The only thing I want to try at this point is the airstone test RHF designed to diagnose what's going on.

 

[GrandmaReefer]

How does your tank look? I’ve got a similar issue - also with Neptune probes - and the tank looks fine. Euphyllia are sulking a bit but other LPS great. Softies don’t care.

I’ve got two Neptune probes, both recalibrated yesterday - showing me 7.88 and 7.78 in the same tank. Alk is 9.1- I’m not dosing alk, just CA.

My co2 scrubber used to work great. Now it seems to have negligible impact.

Only recent change is I turned off my UV. I’ve considered turning it back on but my pod population predictably exploded after stopping and I don’t want to disrupt them. But I did read bacteria can depress PH.

Did a 20% WC - no real impact except to lower alk. I’m stumped.

 

[bubbgee]

How does your tank look? I’ve got a similar issue - also with Neptune probes - and the tank looks fine. Euphyllia are sulking a bit but other LPS great. Softies don’t care.

I’ve got two Neptune probes, both recalibrated yesterday - showing me 7.88 and 7.78 in the same tank. Alk is 9.1- I’m not dosing alk, just CA.

My co2 scrubber used to work great. Now it seems to have negligible impact.

Only recent change is I turned off my UV. I’ve considered turning it back on but my pod population predictably exploded after stopping and I don’t want to disrupt them. But I did read bacteria can depress PH.

Did a 20% WC - no real impact except to lower alk. I’m stumped.

Kalk has been working for me. I am now at 7.9 (low) and hitting 8.13 at peak and I'm just trying to raise it slowly. Alk went high at one point (around 9.7) and I did a 10% water change and resumed kalk dripping. Corals look puffy now and happy at higher pH.

The airstone trick didn't work for me unfortunately.

 

[GrandmaReefer]

Good to know. I’ve got a new probe coming today and if shows the same thing then I’m thinking about following your lead.

This hobby is so fun.