Are decreased dissolved oxygen levels fact-or-ficton with CO2 scrubbers?

chaostactics

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NOTE: I specifically meant recirculating CO2 scrubbers. Not CO2 scrubbers in general.

TL DR. I'd like to run a "recirculating" CO2 scrubber on my skimmer but have heard, what are probably anecdotal, reports that it could drop your dissolved oxygen to dangerous levels.

Long text but I'm trying to give as much detail up front.

I want to bring my over all pH up. Pulling air from outside is absolutely not an option and I already run my lights for my macro algae on reverse cycle to my display.

I'm running an open top 80 gal 32"x24W" with a drilled over flow. It's using a Herbie style overflow so pulling siphon.

The drain ends underwater in my sump. The water in the drain camber then comes up and runs through 2 filter socks then the water goes into chamber 2 consisting of a Essence 130 skimmer and Skimz MBR 157 macro algae reactor.

Then into the return chamber. Flow in the tank is from the Varios S6 return that run to two 0.5" lock line returns terminating in RFGs and two gyre xF350 mounted vertical about 8" below the water surface.

The tank is an SCA 80 and sump is a older Red Sea Reefer 250 sump.

My pH generally runs between high 7.7 and 7.9*. Alk averages mid 6s.

In theory do I have an overall high enough gas exchange elsewhere besides the skimmer to not worry about tanking my dissolved oxygen by mostly "sealing" my skimmer cup lid and drawing the air intake for the CO2 scrubber from inside the skimmer lid?

*The pH probe is a BRS double junction probe that's nearly brand new and was calibrated before being put into service.
SCA-80GPNP-2T.jpg

reefer-250-sump.jpg

Screenshot_20211002-211600_APEX Fusion.jpg
 
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Subsea

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Probably / Could / Antecedal



I suggest you read the link. The absorption media removes carbon dioxide only.

If you wish to increase oxygen, then promoting better gas exchange at all water/air interfaces will directly achieve your goal. Consider cascading water from display overflow to sump.

Another method to increase oxygen & decrease carbon dioxide is to increase photoperiod or intensity of light in your macro refugium.

last method is to feed your protein skimmer pure oxygen from a bottle.
 

Subsea

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This may be more technical than you wish to read. It’s scientific not antecedal. I used degassing columns in 10K gallon coral / live rock growout system in a greenhouse.
 

Dan_P

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TL:DR. I'd like to run a "closed loop" CO2 scrubber on my skimmer but have heard, what are probably anecdotal, reports that it could drop your dissolved oxygen to dangerous levels.
I never heard this one and I don’t see how a CO2 scrubber could remove oxygen. CO2 is removed because it chemically reacts with the basic medium. Oxygen does not react with this medium. If this information you read does not come with an oxygen measurement, I would ignore it.
 

ReefBeta

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The worst case is no new air, thus oxygen, gets into the skimmer. That's not worse than running your tank without the skimmer. So can your tank operate without a skimmer? Most reef tank can.
 

Pistondog

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TL:DR. I'd like to run a "closed loop" CO2 scrubber on my skimmer but have heard, what are probably anecdotal, reports that it could drop your dissolved oxygen to dangerous levels.

Long text but I'm trying to give as much detail up front.

I want to bring my over all pH up. Pulling air from outside is absolutely not an option and I already run my lights for my macro algae on reverse cycle to my display.

I'm running an open top 80 gal 32"x24W" with a drilled over flow. It's using a Herbie style overflow so pulling siphon.

The drain ends underwater in my sump. The water in the drain camber then comes up and runs through 2 filter socks then the water goes into chamber 2 consisting of a Essence 130 skimmer and Skimz MBR 157 macro algae reactor.

Then into the return chamber. Flow in the tank is from the Varios S6 return that run to two 0.5" lock line returns terminating in RFGs and two gyre xF350 mounted vertical about 8" below the water surface.

The tank is an SCA 80 and sump is a older Red Sea Reefer 250 sump.

My pH generally runs between high 7.7 and 7.9*. Alk averages mid 6s.

In theory do I have an overall high enough gas exchange elsewhere besides the skimmer to not worry about tanking my dissolved oxygen by mostly "sealing" my skimmer cup lid and drawing the air intake for the CO2 scrubber from inside the skimmer lid?

*The pH probe is a BRS double junction probe that's nearly brand new and was calibrated before being put into service.
SCA-80GPNP-2T.jpg

reefer-250-sump.jpg

Screenshot_20211002-211600_APEX Fusion.jpg
Can you point us to your anecdotal sources?
This might help to debunk or verify the claims.
 
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chaostactics

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@Pistondog



 
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Pistondog

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@Pistondog



As @Subsea said increasing co2 removal via photosynthesis increases ph.
If your ambient air is high in co2, perhaps turning off the skimmer during the day might increase your ph. It was an unintended effect of running my skimmer only at night. During the day, skimmer off, the co2 reduction via photosynthesis wasn't replenished by the skimmer air exchange, and the max ph at lights out rose from 8.35 to 8.4.
Easy to,try.
 
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chaostactics

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As @Subsea said increasing co2 removal via photosynthesis increases ph.
If your ambient air is high in co2, perhaps turning off the skimmer during the day might increase your ph. It was an unintended effect of running my skimmer only at night. During the day, skimmer off, the co2 reduction via photosynthesis wasn't replenished by the skimmer air exchange, and the max ph at lights out rose from 8.35 to 8.4.
Easy to,try.
My worry is going to be salinity shift associated with running a skimmer in that manner. Having the skimmer off will cause a rise in the sump water level which will rapidly reverse when the skimmer is activated. I will end up with a large freshwater bolus when the ATO goes to catch up. Maybe the amount of shift isn't significant though...
 

Pistondog

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My worry is going to be salinity shift associated with running a skimmer in that manner. Having the skimmer off will cause a rise in the sump water level which will rapidly reverse when the skimmer is activated. I will end up with a large freshwater bolus when the ATO goes to catch up. Maybe the amount of shift isn't significant though...
In my case, I don't think it's significant. But a good thought.
 

taricha

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I think, yes. if you plumb it to recirculate the same air, then you are cutting off the skimmer as an aerator for oxygen into the water. And that's one of the best avenues for O2 to get into the water.
I don't know how much flow and O2 you'd have without it, and it'd be really hard to say without measuring - that it is or isn't a problem.
 

2una

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My pH generally runs between high 7.7 and 7.9*. Alk averages mid 6s.

Why don't you raise your dkh to something closer to 8 & see if that don't help out?
Without going overboard running your display lighting longer or more intense can also help.
Larger skimmer can also be worth a try
 

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