CO2 Scrubber - humidity and media absorption capacity

reefiniteasy

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I use a medium IceCap CO2 scrubber plumbed to my Aquamaxx HOB 1.5 skimmer. My tank does not drop below 8 at night and gets as high as 8.24ish to 8.3ish after my daily manual dosing. Before using the scrubber I would hover between 7.7-7.9 and it would drop considerably at night. When I first started to use the scrubber I would only get two to three weeks on the media. Then I saw a post here on the forum that said adding water to the scrubber would increase the humidity and allow the media to absorb more. So I make sure there is always 20ml of water in the bottom of the scrubber. I went with 20ml because that’s the syringe I had. Making sure there is constant water in the scrubber has allowed me to go 4 weeks, from Sept. 18 to Oct. 17, on the same batch of scrubber media. Why did the water help? Does it increase absorption? Any ideas!

I really want to maximize my media usage. I know I can make the scrubber recirculating but I’m not sure I need to. Here is a graph showing the last couple days of that 4 week period and the start of the new batch of CO2 media.

9608D27C-D9A5-426B-A90C-FFAA2FC21FC7.png
 

Memisis

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Following this thread.

One comment, when I did a tight closed recycle loop from the skimmer to the media the air was moist as there was slight condensation thought the loop. However I found that after a few days there was a negative impact to the skimmers ability to skim. I have since removed the loop and get 3-4 weeks from a canister. The skimmer is also creating really great skimmate. My next move will be to put in the Avast auto squeegee to really get the most skimming possible.

Keep us updated with your progress and findings.
 

jgirardnrg

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I use a doser and just dose RODI in the CO2 scrubber daily. I'm going to do the same thing with the new tank I'm setting up in my build thread. I'm not sure of the science behind it but I do know that it's said that the air needs to be humid. I haven't gauged how long my media lasts... I just keep an eye on it and swap it out when it's exhausted.
 

Joe31415

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Following this thread.

One comment, when I did a tight closed recycle loop from the skimmer to the media the air was moist as there was slight condensation thought the loop. However I found that after a few days there was a negative impact to the skimmers ability to skim. I have since removed the loop and get 3-4 weeks from a canister. The skimmer is also creating really great skimmate. My next move will be to put in the Avast auto squeegee to really get the most skimming possible.

Keep us updated with your progress and findings.
One of the protein skimmer manufactures mentioned exactly this. That setting up a recirculating CO2 Scrubber had a negative impact on the skimmer.
Personally, I went with a middle option. I ran a tube from the intake to the CO2 scrubber to the skimmer lid. Not in it, I just have it sitting right next to or on top of it. I figure that gives it some air from the skimmer and some fresh air.
 

Gedxin

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I don't recirculate nor do I put any water in my scrubber. Indoor humidity is usually around 45% and certainly higher in the sump area. Media lasts about 3-4 weeks before I notice my pH staying around 8 instead of typical 8.2ish during the day.
 

Randy Holmes-Farley

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I'm not a fan of recirculation since it stops an important aspect of a skimmer, IMO: oxygenation.

As to the original question, moisture puts a very thin coating of water on the media surface, allowing for easier attachment of CO2 to the surface, movement of ions on the surface, and movement into a very thin dissolved layer of material that can reorganize into calcium carbonate.
 

DivingTheWorld

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I'm not a fan of recirculation since it stops an important aspect of a skimmer, IMO: oxygenation.
Can I ask how it stops oxygenation? Note: I am NOT a scientist and just genuinely curious. If you recirculate your Skimmer, shouldn’t the air in your Skimmer have more oxygen, not less since the scrubber is removing the CO2?

If the recirculation eliminates oxygenation and the CO2 scrubber removes CO2, what exactly is running through the Skimmer, pure Hydrogen?

As for mechanical function of the Skimmer, I run my scrubber intake from the lid of my Skimmer and have found no reduction in Skimmer mechanical function.
 

Memisis

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Can I ask how it stops oxygenation? Note: I am NOT a scientist and just genuinely curious. If you recirculate your Skimmer, shouldn’t the air in your Skimmer have more oxygen, not less since the scrubber is removing the CO2?

If the recirculation eliminates oxygenation and the CO2 scrubber removes CO2, what exactly is running through the Skimmer, pure Hydrogen?

As for mechanical function of the Skimmer, I run my scrubber intake from the lid of my Skimmer and have found no reduction in Skimmer mechanical function.

I think of it like breathing. If you breath recirculating air, you will deplete the oxygen eventually. This would result in less oxygenation since the skimmer has such great potential to oxygenate and that potential would be lost. We would need to give the skimmer a breath of fresh air every so often.
 

Randy Holmes-Farley

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Can I ask how it stops oxygenation? Note: I am NOT a scientist and just genuinely curious. If you recirculate your Skimmer, shouldn’t the air in your Skimmer have more oxygen, not less since the scrubber is removing the CO2?

If the recirculation eliminates oxygenation and the CO2 scrubber removes CO2, what exactly is running through the Skimmer, pure Hydrogen?

As for mechanical function of the Skimmer, I run my scrubber intake from the lid of my Skimmer and have found no reduction in Skimmer mechanical function.

It stops oxygenation simply by not adding any more than is already there. Ever.

Recycling the same air over cannot add any O2, even at night when it is low in the water and may be beneficial.

If you use new air each time, it always has the same natural amount of O2 in it, and if the tank drops as night, the skimmer will add O2 into the water.
 

Randy Holmes-Farley

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I think of it like breathing. If you breath recirculating air, you will deplete the oxygen eventually. This would result in less oxygenation since the skimmer has such great potential to oxygenate and that potential would be lost. We would need to give the skimmer a breath of fresh air every so often.

Good analogy. :)
 

DivingTheWorld

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It stops oxygenation simply by not adding any more than is already there. Ever.

Recycling the same air over cannot add any O2, even at night when it is low in the water and may be beneficial.

If you use new air each time, it always has the same natural amount of O2 in it, and if the tank drops as night, the skimmer will add O2 into the water.
If the system is totally sealed I would agree, but in our aquariums it never is. There is water flowing through the skimmer. There is also (at least in my RO skimmer) vent holes in the skimmer cup lid. And finally, my skimmer outlet pipe blows out air which is replaced from...somewhere?

But back to my original question, IF the system is completely sealed, what is pumping through your skimmer if you're using a recirculating CO2 scrubber? Assuming your air is Nitrogen, Oxygen (and 1% Argon), recirculating the skimmer air will continually draw out CO2. Assuming as you say it also no longer contains Oxygen, are you only recirculating pure Nitrogen? Clearly the air in a recirculating CO2 scrubber contains far less CO2 because the media lasts at least 2x longer (from my personal observations).

Then there is the question of how it actually effects the Oxygen content of your tank water. If indeed it is continuing to pull CO2 out of your tank water, wouldn't that in effect be increasing the Oxygen % of your tank water? One replaces the other right?

A tank like mine, rimless with an open top, an open sump and huge flow, there is significant air exchange even without a skimmer.

Has anyone actually measured the Oxygen content of their tank water before and after installing a recirculating CO2 scrubber?
 
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reefiniteasy

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I use a doser and just dose RODI in the CO2 scrubber daily.

Excellent idea! I’ve been looking to start dosing 2-part instead of manually dosing everyday. Maybe I’ll look for a multi-head dosing pump so I can dose water to the scrubber. Thank you for sharing.

As to the original question, moisture puts a very thin coating of water on the media surface, allowing for easier attachment of CO2 to the surface, movement of ions on the surface, and movement into a very thin dissolved layer of material that can reorganize into calcium carbonate.
Couple questions…

The CO2 only attaches to the surface of the media?

The more surface area, the more the media holds?

The center of the media, beyond the surface goes unused?

Beyond adding water, the only way to increase attachment to the surface is to use more media?

Thanks Randy!
 

jgirardnrg

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Excellent idea! I’ve been looking to start dosing 2-part instead of manually dosing everyday. Maybe I’ll look for a multi-head dosing pump so I can dose water to the scrubber. Thank you for sharing.
I have a 4 head doser that I use for Alk, Ca, Mg and the 4th head does the RODI. Then I have a 2 head for dosing aminos etc.

If you're planning on dosing, don't go cheap with the doser you select. I have two 4 head units that sit on a shelf because they cannot be trusted. I also use the Kamoer X1 Pro single head dosers on my frag tank. When/if I need another head I just grab another unit at around $80. They keep calibration and don't lose prime for me. The cheap ones I bought were a waste of money.
 

Randy Holmes-Farley

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If the system is totally sealed I would agree, but in our aquariums it never is. There is water flowing through the skimmer. There is also (at least in my RO skimmer) vent holes in the skimmer cup lid. And finally, my skimmer outlet pipe blows out air which is replaced from...somewhere?

But back to my original question, IF the system is completely sealed, what is pumping through your skimmer if you're using a recirculating CO2 scrubber? Assuming your air is Nitrogen, Oxygen (and 1% Argon), recirculating the skimmer air will continually draw out CO2. Assuming as you say it also no longer contains Oxygen, are you only recirculating pure Nitrogen? Clearly the air in a recirculating CO2 scrubber contains far less CO2 because the media lasts at least 2x longer (from my personal observations).

Then there is the question of how it actually effects the Oxygen content of your tank water. If indeed it is continuing to pull CO2 out of your tank water, wouldn't that in effect be increasing the Oxygen % of your tank water? One replaces the other right?

A tank like mine, rimless with an open top, an open sump and huge flow, there is significant air exchange even without a skimmer.

Has anyone actually measured the Oxygen content of their tank water before and after installing a recirculating CO2 scrubber?

There's nothing controversial about my claim of no oxygenation from recirculating skimmer air, except how low the O2 would get at night and how high it would get during the day without the gas exchange a skimmer causes (and whether either value is significant). The basic process effects are simple chemistry (Raoult's Law).

FWIW, no one claimed that there is no O2 in the recirculating air. If there's was somehow, that would be a disaster.

In a closed system of recirculating air, the air will track the O2 level in the water. It will never get super low, but also will never add much just because the tank water dropped in O2.

Water flowing through the skimmer is not relevant, since it is what is potentially going to be low in O2 to begin with.

CO2 entering or leaving the water has zero effect on O2 or any other gas (except an acidic or basic gas such as ammonia).

As far as I know, I am the only one to point out the basic chemistry problem of a recirculating skimmer, and it was never used much until BRS (not chemists) began to push the idea. SO I know of no data on O2 in recirculating skimmers.

But there is data on O2 in skimmerless vs skimmed tanks, so it is clear that in some cases, skimmers do help bring up low O2 levels at night:


"Aquaria can and do become hypoxic at night and such a state may pose a risk to hypoxia-intolerant organisms. Cloudy water in shipping containers and tanks is a cause for concern as oxygen levels are measured to decline rapidly and to very low levels."

"Airstones and skimmers appear to be a very effective means of oxygenating small water volumes. Their effect on larger water volumes appears to be less. While the effect may be relative, the larger tanks and systems described here utilized powerful skimming or air pumps, and to gain an equivalent amount of oxygen as occurs in small water volumes would likely require air pumps or skimmers far larger than those commonly employed by aquarists."
 

Randy Holmes-Farley

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Excellent idea! I’ve been looking to start dosing 2-part instead of manually dosing everyday. Maybe I’ll look for a multi-head dosing pump so I can dose water to the scrubber. Thank you for sharing.


Couple questions…

The CO2 only attaches to the surface of the media?

The more surface area, the more the media holds?

The center of the media, beyond the surface goes unused?

Beyond adding water, the only way to increase attachment to the surface is to use more media?

Thanks Randy!

The media may have pores in it that CO2 can enter, but assuming you consider the inside of these pores to be "surface" then yes, that is all true.
 

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