Relationship between O2, CO2, and PH

[Cas8100]

I'm hoping that the community can help me understand the relationship between O2, CO2, and PH...

It's my understanding that a high CO2 concentration will cause a drop in PH. I've seen it recommended that one solution to low PH is to increase surface agitation or to add a fresh air intake to the skimmer to help promote gas exchange and help the tank rid excess CO2. In this case, if CO2 is high, does it also mean that the oxygen/O2 levels are low?

To frame the question a different way... I have been reading that one side effect of using a red slime remover is that the reaction rids the tank of oxygen very quickly. Because of this, the manufacturer recommends the use of an air stone before, during, and after treatment. If the O2 levels, drop, should I see a corresponding decrease in PH as the percentage of CO2 increases?

To frame the question a 3rd way, does an increase in CO2 always result in a decrease in O2...and does an increase in O2 always result in a decrease in CO2?

Thanks in advance for straightening me out...

Regards,
CS

 

[bertoni]

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There's no relationship between oxygen and the pH level. Carbon dioxide will lower the pH as it dissolves into the water. The carbon dioxide level doesn't affect the oxygen level, either. Our houses tend to have a fair amount of carbon dioxide in the air, so the pH in our tanks runs low, but oxygen is generally at saturation.

 

[Cas8100]

Thanks.. so what is the cause for the diurnal swing in pH? I had thought as plants gassed oxygen during photosynthetic hours, o2 increased, resulting in the increase in pH. Perhaps the ph increase is driven by plant life absorbing some of the dissolved co2 instead?

 

[bertoni]

As you suggested, photosynthesis consumes carbon dioxide from the water column, which drives the pH up. The carbon goes into sugar, or other carbohydrates.

 

[Cas8100]

Thanks. Are there any ways that people can measure and track the percent of O2 saturation in the water?

 

[disc1]

Thanks. Are there any ways that people can measure and track the percent of O2 saturation in the water?

If you have a skimmer then O2 is most likely supersaturated in your tank. You can count on it at least being at the saturation point.

 

[bertoni]

I measured oxygen in my tanks using a Salifert kit for a while. The levels I measures were always at saturation.

 

[Tripod1404]

There is 21% O2 and ~0.04% CO2 in atmosphere. So a skimmer can easily saturate water with O2. Inside of houses tend to have higher CO2 (like 0.06%) and sightly lower O2 (~18%), but it is still highly abundant and therefore saturated in water.

 

[tjnorthdakota]

there is a indirect affect of less oxygen in the tank to ph, with less oxygen in the tank there will be more anaerobic bacteria producing elevated levels of co2, so the less oxygen the more co2

 

[jason2459]

there is a indirect affect of less oxygen in the tank to ph, with less oxygen in the tank there will be more anaerobic bacteria producing elevated levels of co2, so the less oxygen the more co2

I'd be interested in where you got that information from?

 

[Reefable]

I am also trying to get my head around this issue. Since I moved my sump to the basement I have been constantly battling s very low ph. It's between 7.37 to 7.45 range. Did everything I could external airline to the skimmer, 24hrs photosynthesis over my refugium, dose Kalkwasser as an ATO but no luck. As per the posts above O2 levels are always at Saturated levels compared to CO2 so why am I not seeing my PH go up? The flow is strong through my refugium so there is enough surface agitation there. CONFUSED and not sure what else can guys like me do?


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[bertoni]

The oxygen level doesn't affect the pH. I'd guess there's some sort of measurement problem in this case, because 7.37 is very low, but the issue is carbon dioxide. It's quite possible to have very low pH levels with full oxygen saturation. It's very common, actually.

 

[Reefable]

Thanks Bertoni I did recaliberated the probe last week though. I am just at loss as to how to fix this issue. PH tht low could cause a tank to crash but mine is thriving and I have ran out of any alternatives.


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[bertoni]

As long as the animals are okay, I wouldn't worry all that much. There might be some electrical interference that is interfering with the readings, so if you'd like to experiment some, measuring a water sample well away from the tank might be interesting. If the meter is plugged into the same circuit as the tank, or the wires are close to other power lines, that might be an issue, too.

 

[Reefable]

Thanks I will try to test the water away from the tank but you r right the apex is plugged into the same circuit as the tank. The other thing I would like to know is how long does it take to see any adverse effects on the corals and fishes due to low ph?


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[bertoni]

If the pH gets low enough, I'd expect animal deaths in a short period, but mostly I'd expect low or no growth in corals as the primary sign of problems.

 

[Reefable]

Ok thanks Bert. Here is the update just to test if the probe isn't an issue I tested it in my Still Kalkwasser reservoir and the Ph showed 11.8 which makes sense as Kalkwasser ph at full saturation is 12. Than I tested the sump water away from the sump tank and the ph showed in the range of 7.5 than I took the water from my display which is a floor above (fmly room) and the Ph showed 8.2 sooo this tells me the sump ph is low due to CO2 since it's in the furnace room however the ph of my display is in the range of 8.0-8.2. Should I b worried ?


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[bertoni]

Okay, that makes sense. As long as the display tank is at 7.8 or above, I wouldn't worry.

 

[Reefable]

Okay, that makes sense. As long as the display tank is at 7.8 or above, I wouldn't worry.

Great yeah I am gonna leave it at tht...I would move my apex probe upstairs to make sure I see s good reading rather than downstairs


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[Cas8100]

Ok thanks Bert. Here is the update just to test if the probe isn't an issue I tested it in my Still Kalkwasser reservoir and the Ph showed 11.8 which makes sense as Kalkwasser ph at full saturation is 12. Than I tested the sump water away from the sump tank and the ph showed in the range of 7.5 than I took the water from my display which is a floor above (fmly room) and the Ph showed 8.2 sooo this tells me the sump ph is low due to CO2 since it's in the furnace room however the ph of my display is in the range of 8.0-8.2. Should I b worried ?


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Is it normal for there to be a discrepancy in pH between sump water and display tank water? I would think that with a turnover rate of maybe 10x per hour, the water exchange would be happening faster than any differential gas exchange.