pH low and possibly dropping

[ctyler85]

My pH is sitting about 7.77 during the day and 7.56 at night. I posted this question in my local forum and the answer I got was excess co2 and everyone said to dose kalk or run a co2 scrubber. How do I know this is the cause, and if this is the cause shouldn't I go after the cause of the co2 buildup? I have calibrated my pH probe and used a second pH meter and they both are reading the same. Everything in the tank still looks relatively happy. After reading about co2 build up it only left me scratching my head even more. There is plenty of surface disruption from the power heads, the overflows are skimming well, the drain side of the sump is bubbling like crazy, skimmer is going well and producing a lot of bubbles, I have a power head in the fuge pointed at the surface. Alk is still OK. 8dkh, calcium is 460ppm. At first I was going after it with the alk side of the 2 part which only got me to 7.9ph and 9dkh dosed calcium to bring the alk back down but then the calcium was over 500ppm so I stopped with all that. Is there another way to get my pH up? Is there another underlying cause I need to correct? Should I try baking soda?

 

[Randy Holmes-Farley Verified Community Expert]

The ONLY causes of low pH in seawater are low alkalinity or high CO2. Together, those two mathematically determine the pH in seawater.

Assuming your alkalinity and pH measurements are correct, then the excess CO2 is probably coming from your home air, although it could also just be in the tank water if you have poor aeration. The article below gives an aeration test to see if it is just the tank water, or if the room air also has too much CO2.

DO NOT ADD BAKING SODA. It will lower pH, and raise alkalinity.

Before doing anythign else, I'd recalibrate the pH meter with new pH buffers.

If the pH still is that low, I'd look to limewater (kalkwasser) or getting fresher air to the tank. That could be a scrubber, or bringing in outside air, either to a skimmer inlet, or to the whole room.

This has more:
Low pH: Causes and Cures by Randy Holmes-Farley - Reefkeeping.com

 

[ctyler85]

Thanks Randy.

 

[ctyler85]

We did have the windows open for a few days when the weather was nice, and no change, I like the idea of running an airline to the outside but this would end up being a very difficult task. I am assuming a co2 scrubber on the skimmer air inlet would also help this out? I'm going to see if I can source any kalk locally

 

[Randy Holmes-Farley Verified Community Expert]

Yes, a scrubber works.

But if the windows were open and it didn't help, that suggests the pH meter may be inaccurately calibrated and I'd check that first. Then do the aeration test in the article.

 

[ctyler85]

I recalibrated it once already and compared with a second meter. I'm going to recalibrate it again tonight

 

[Randy Holmes-Farley Verified Community Expert]

Ok. The calibration buffers can also go bad, although that usually causes pH to read too high as they absorb CO2.

 

[ctyler85]

So here's something interesting. Did the aeration test. Starting pH 7.9 ( forgot to take sample water before starting the drip dosing of kalk) aeration outside 7.7pH scratch my head, aeration inside the house dropped from 7.9 to 7.7. But the kalk seems to be doing the trick, so far pH is holding at 8.2

 

[Randy Holmes-Farley Verified Community Expert]

That outside testsuggests to me that perhaps the pH meter in calibrated too low, and the pH is actually higher than you think, but raising it somewhat is generally not a concern.

 

[ctyler85]

Good deal. I'll order some new calibration packets. After dosing the kalkwasser as a top off the pH did spike (according to the controller) to 8.4, over the night it seemed to level off at 7.9, everything's polyps exploded. Alk is on the high end at 11.5dkh. I'll keep an eye on it today and hopefully the pH holds

 

[Randy Holmes-Farley Verified Community Expert]

Good deal. I'll order some new calibration packets. After dosing the kalkwasser as a top off the pH did spike (according to the controller) to 8.4, over the night it seemed to level off at 7.9, everything's polyps exploded. Alk is on the high end at 11.5dkh. I'll keep an eye on it today and hopefully the pH holds

That part all seems reasonable.