Calcium Reactor pH Probe Reading Low

[newtosps]

Hi All,

I am having an odd issue with my calcium reactor. I have read a couple of threads on here relating to an abnormally high pH reading within some reefers' calcium reactors that was possibly explained by a wash applied to the media, as the pH seemed to stabilize after a few days, but I am currently experiencing the opposite issue - a low pH reading in the reactor when measured with a Neptune Apex pH probe.

I am currently running a Reef Octopus CR-140 calcium reactor containing ARM extra course media. The reactor has been set up about a year and had been running really nicely, well tuned with a effluent alk of around 25, at effluent rate of 30ml/min and reactor pH 6.25-6.3. Apex never intervened (monitored to detect any major issues) and alk rock solid. Recently I had to swap out the AQ-2000 recirc pump as it failed (I didn't think it was quite right from the word go - but that's another story) and took the opportunity to have a clean and top up the media. On starting the reactor back up (pH probe stored in electrolyte storage solution) I got a pH of 7.0 maximum (tank pH 8.3) and consistently the pH probe is reading around 1.3 pH units lower than what I believe to be the true reading. For example, pH currently reading 5.4 (!) with a C02 bubble rate of only 8/min and effluent alk of 10 (so I know its not really 5.4), also the tank pH has not dropped, all inhabitants doing fine apart from my alk is dropping over the course of the day that I am currently supplementing by dosing (correlating with the reduction id effluent dKH). I have also tested the effluent pH by colorimetric methods e.g phenol red hanna checker and it is reading 6.9, which seems more plausible given the effluent alk and media that is not disintegrating. Any ideas what would cause this?!? So far I have:

• Recalibrated the pH probe with 4.0/7.0 standards
• Swapped out the reactor pH probe for the tank probe - reading still low
• Swapped out pH probe for a spare - no change
• Turned off recirculation pump and nearby electronics in case of some odd voltage leak - no effect (set up is the same prior to the issue anyway)
• Taken a small sample of tank water and, whilst everything running, measuring the pH of that with the reactor probe - measures correctly around 8.3

I am at a loss. Given the colorimetric testing seems to read (more) true, is this an ionic oddity as I know pH probes measure potential difference?

Currently I am dialing the reactor back in using the effluent alk as a guide and the effluent alk seems to be increasing appropriately as I gradually increase the Co2 leaving effluent rate (via peristaltic pump) the same. The difference between probe pH and hanna pH seems constant at 1.3.... any thoughts?

Oh and I only cleaned the reactor using RODI.

Thanks

John

 

[Chrisv.]

Hi All,

I am having an odd issue with my calcium reactor. I have read a couple of threads on here relating to an abnormally high pH reading within some reefers' calcium reactors that was possibly explained by a wash applied to the media, as the pH seemed to stabilize after a few days, but I am currently experiencing the opposite issue - a low pH reading in the reactor when measured with a Neptune Apex pH probe.

I am currently running a Reef Octopus CR-140 calcium reactor containing ARM extra course media. The reactor has been set up about a year and had been running really nicely, well tuned with a effluent alk of around 25, at effluent rate of 30ml/min and reactor pH 6.25-6.3. Apex never intervened (monitored to detect any major issues) and alk rock solid. Recently I had to swap out the AQ-2000 recirc pump as it failed (I didn't think it was quite right from the word go - but that's another story) and took the opportunity to have a clean and top up the media. On starting the reactor back up (pH probe stored in electrolyte storage solution) I got a pH of 7.0 maximum (tank pH 8.3) and consistently the pH probe is reading around 1.3 pH units lower than what I believe to be the true reading. For example, pH currently reading 5.4 (!) with a C02 bubble rate of only 8/min and effluent alk of 10 (so I know its not really 5.4), also the tank pH has not dropped, all inhabitants doing fine apart from my alk is dropping over the course of the day that I am currently supplementing by dosing (correlating with the reduction id effluent dKH). I have also tested the effluent pH by colorimetric methods e.g phenol red hanna checker and it is reading 6.9, which seems more plausible given the effluent alk and media that is not disintegrating. Any ideas what would cause this?!? So far I have:

• Recalibrated the pH probe with 4.0/7.0 standards
• Swapped out the reactor pH probe for the tank probe - reading still low
• Swapped out pH probe for a spare - no change
• Turned off recirculation pump and nearby electronics in case of some odd voltage leak - no effect (set up is the same prior to the issue anyway)
• Taken a small sample of tank water and, whilst everything running, measuring the pH of that with the reactor probe - measures correctly around 8.3

I am at a loss. Given the colorimetric testing seems to read (more) true, is this an ionic oddity as I know pH probes measure potential difference?

Currently I am dialing the reactor back in using the effluent alk as a guide and the effluent alk seems to be increasing appropriately as I gradually increase the Co2 leaving effluent rate (via peristaltic pump) the same. The difference between probe pH and hanna pH seems constant at 1.3.... any thoughts?

Oh and I only cleaned the reactor using RODI.

Thanks

John

Is your CO2 controlled by a solenoid that's coordinated by your apex? At that low of a pH I'm wondering why there is CO2 entering the reactor at all.

 

[newtosps]

Is your CO2 controlled by a solenoid that's coordinated by your apex? At that low of a pH I'm wondering why there is CO2 entering the reactor at all.

Yes the CO2 is controlled by a solenoid via Apex but the issue is the pH probe is, for a reason I cannot get to the bottom of, incorrectly reading the pH as low - the pH cannot be around 5 with an effluent dKH of 10-12, media that isn't turning to mush and colorimetric pH tests (phenol red and now litmus and universal indicator) reading around 6.5-7. The probe read pH is slowly increasing (I think) so it looks as if there may be an odd interference perhaps by something the media has been washed on (?). I thought i'd post as there have been reports of the reverse, abnormally high pH reported.

 

[Chrisv.]

Yes the CO2 is controlled by a solenoid via Apex but the issue is the pH probe is, for a reason I cannot get to the bottom of, incorrectly reading the pH as low - the pH cannot be around 5 with an effluent dKH of 10-12, media that isn't turning to mush and colorimetric pH tests (phenol red and now litmus and universal indicator) reading around 6.5-7. The probe read pH is slowly increasing (I think) so it looks as if there may be an odd interference perhaps by something the media has been washed on (?). I thought i'd post as there have been reports of the reverse, abnormally high pH reported.

I may have missed this: If you take the prove out of the reactor and run it in your tank, is the ph still out of wack? I see that you have already swapped probes and had the same result.

 

[reeftivo]

that reactor has some head space above the top recirc outlet pipe. wondering if there is a pocket of CO2 that may be constantly accumulating at the lid that's affecting the probe. Hmm?

I'd look with a flash light into the reactor under the lid to see of you have CO2 or air pooling up. The reactor could also pull air from seals and lid that is not tight enough.

If so, I would shut off the CO2 and hand dose for a while, then run the feed pump and the recirc pump wide open for a day. that will expel the air/gas.

edit: are you pulling with a peristaltic or pushing with power head for the feed?
pulling with peristaltic can draw air into reactor if things are not tight. pushing will usually show leaks outside the reactor.

 

[HuduVudu]

PH probes are notoriously innaccurate. I wouldn't trust the probe.

I think the more important thing is that your effluent is 25dKH. As long as this holds true I wouldn't worry much.

You might want to at this point make sure that you note your effluent and bubble count so that you can get a golden ratio.