CO2 scrubber: nonsense?

KenRexford

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Now that I have a controller, here’s what I have seen over the past week.

I had my CO2 scrubber working with relatively fresh media. The pH results were steady.

I then added a recirculating device. The pH slightly DROPPED on average.

Then, I took the entire CO2 scrubber off, and my pH increased to a nicer level.

I swear that the more CO2 scrubbing “power,” the worse my pH.
 

Gedxin

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Are you monitoring the CO2 in the tank room? A scrubber is only going to help if there are elevated CO2 levels and your water is absorbing more. What about open windows?

Also a recirculating system is not often recommended, there are a lot of mixed stories on its benefits.
 
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MnFish1

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Now that I have a controller, here’s what I have seen over the past week.

I had my CO2 scrubber working with relatively fresh media. The pH results were steady.

I then added a recirculating device. The pH slightly DROPPED on average.

Then, I took the entire CO2 scrubber off, and my pH increased to a nicer level.

I swear that the more CO2 scrubbing “power,” the worse my pH.
First - when you say the pH went up - or down - how much are we talking? Second what is a recirculating device? third - you need to at least consider that your controller is 'wrong' (i.e. not measuring the correct pH). I would suggest the solution to the question is to not change so many variables. Measure the pH with the scrubber attached - and measure it with the scrubber off. And double check the monitor with a separate test?

and as others have said - opening a window will alter the pH - but I don't think it will help tell you whether your scrubber is helping or not.
 

ScottB

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Others have touched on this and maybe I can narrow it down. The utility of a scrubber is affected by a few things:
a) Ambient CO2 in the house. Mine varies from 394ppm to 800ppm.
b) Size of skimmer relative to system. An oversize skimmer can help more than an undersized.
c) If the skimmer pulls air easily from outdoors, you can ignore (mostly) "a".
d) Recirc helps if you can't do "c", but it isn't perfect. The best is outdoor pull to oversize skimmer. Unless you live just northeast of New York City or downwind of other major metro.

If you have a large system and really low pH, you could switch to kalk dosing. It takes a lot of refining to get it right, but it is infinitely more capable than a scrubber IME.

I really tried to make a scrubber work but it simply wasn't feasible in my situation. Kalk stirrer and APEX DOS for the win. Here is my pH chart for the last week. Every other Sunday, I dump a cup of calcium hydroxide into the stirrer.

1635288653924.png
 
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KenRexford

KenRexford

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I have doors and windows closed. Chilly up here in Ohio. The impact of the changes was obvious. The wave moved. Top lower with scrubber recirculating, highest when scrubber off. Low reading moved exactly the same amount.

Here’s my layman’s theory. If the CO2 in the room is high, maybe a scrubber works. If the CO2 in the room is naturally fine, then the scrubber is somehow causing the protein skimmer to have slightly different bubble size. The effect is to have skimming ability increase but oxygen exchange decrease, relative to each other. The impact would then, in my layman’s theory, be that the foaming set to the right level for skimming effectively translates into lessened introduction of fresh oxygen.
So, being more imprecise and potentially insane, the scrubber might cause, say, stickier big bubbles. More gunk, less oxygen exchange. Increase the effectiveness of the scrubber by recirculating, bigger, stickier bubbles, even less oxygen. Remove both, smaller, less sticky bubbles, but more oxygen exchange.
 
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KenRexford

KenRexford

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Well, this is funny:
Apparently the size of bubbles in the actual ocean, which varies depending upon complicated circumstances, seems to in fact have an impact on the ration of saturation of CO2 vs O2. Thus, if something about the scrubber is in fact changing the bubble size somehow, it may be causing bubble sizes that are “pro CO2” while a skimmer without the scrubber creates bubbles that are “pro O2,” which would seem to vent off CO2 better and thus increase pH.
The question might then be how attaching a scrubber might affect bubble size.
Thinking out loud, maybe the mechanism is strangely counter-intuitive. Suppose that this is sort of a Laugher Curve. Bubble size from a protein skimmer might be ideal for oxygen dissolving and CO2 gassing at a specific ratio of CO2 to O2. Increase the CO2 (dirty house air) and the bubble size is pro CO2. Increase the O2 instead, and again the bubble size is pro CO2. With too much CO2 from the source, the exchange is pro CO2, so reduction of CO2 gets to the right exchange for pro O2. However, if the air is already good, increasing the O2 too much kicks the bubble size to a different type of pro CO2. The three little bears theory of protein skimmers and scrubbers?

Those seeing benefits from the scrubber but then negative from the recirculating are tweaking too far.

A possible result set, then:
Really dirty air? Scrubber plus recirculating creates the best bubble size, pro-O2, venting CO2. Scrubber alone, not as good. No scrubber, bad.
Somewhat dirty air? Scrubber is the sweet spot on bubble size. No scrubber is worse, but recirculating is also worse because the bubbles get too small/large from the combined effects.
Clean air? Scrubber messes with the bubble size and hurts pH level. Recirculating compounds and worsens the problem.
Room with too much O2 for some reason? Strangely, dosing a small amount of CO2 into the protein skimmer intake would then ironically increase pH by changing the bubble size.
 

Randy Holmes-Farley

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CO2 scrubbers are certainly not nonsense, as the title asks, but they may not be the best way to raise pH in many settings.

I'm not a fan of recirculating air. Not because of CO2 and pH effects, but because it eliminates the benefit of oxygenation in the skimmer. Some proponents seem to be unaware of this concern.

How much (if any) effect one sees from a skimmer with outside air or scrubbed air depends strongly on the relative aeration effects of the skimmer vs all other parts of the tank thst are still in the high CO2 air, such as the tank top.
 

Randy Holmes-Farley

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A possible result set, then:
Really dirty air? Scrubber plus recirculating creates the best bubble size, pro-O2, venting CO2. Scrubber alone, not as good. No scrubber, bad.
Somewhat dirty air? Scrubber is the sweet spot on bubble size. No scrubber is worse, but recirculating is also worse because the bubbles get too small/large from the combined effects.
Clean air? Scrubber messes with the bubble size and hurts pH level. Recirculating compounds and worsens the problem.
Room with too much O2 for some reason? Strangely, dosing a small amount of CO2 into the protein skimmer intake would then ironically increase pH by changing the bubble size.

I do not see how that makes any scientific sense, and I think several of the assumptions are not correct.

How would dosing a small amount of CO2 into a skimmer increase the bubble size?

If somehow you had a bubble with so much CO2 in it that it appreciably increased the bubble size (say, by 50% in volume), that is a MASSIVE amount of CO2 in terms of partial pressure, which will drive the pH down by MANY pH units. Normal air has about 400 ppm CO2. To double a bubble volume requires that more than 500,000 ppm of the air in the bubble be CO2, for a whopping increase in CO2 of more than 1,000x.
 

arking_mark

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A skimmer increases tank aeration and pushes pH towards equilibrium with the air intake CO2 regardless of bubble size and O2. Skimmer air is probably as clean as your indoor air and wouldn't impact anything.

There are many explanations to why you may have your unexpected results as house CO2 levels can drastically change day to day and hour to hour. How long and when did you test each setup? How much CO2 scrubbing media are you using? Is your skimmer aeration strong enough to significantly impact pH? Etc...

I would do a cup aeration test to verify adequate tank aeration and higher indoor CO2.

I would then suggest the following experiment.

No skimmer for two weeks. This should give you a baseline for your daily pH swings.

Skimmer for two weeks. Assuming higher indoor CO2, you should expect to see lower pH highs.

Skimmer with CO2 scrubber and fresh media for 2 weeks. Assuming higher indoor CO2, you should expect to see higher average pH.

Skimmer with recirculating CO2 scrubber and fresh media for 2 weeks. Assuming higher indoor CO2, you should expect to see even higher average pH.

It is possible that your tank aeration from pumps/powerheads circulation far exceeds the ability of your skimmer and your skimmer may have little impact on your pH. It may still be good for filtration.

I use my skimmer just for pH control and needed to oversize it to get my desired control.

 
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KenRexford

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I have been monitoring pH for some time, and the effects that I am noticing seem fairly certain. There seems to be some shared experience from others in this regard, inconsistent with others. The bubble size impact seems to have been studied, per my link, and is real. So, maybe there’s a different cause. If the phenomenon is real, there might be a fix.

Suppose it’s as simple as the specific model of skimmer and the motor type having to run slightly different due to back pressure from the tubing, scrubber, and recirculating all forcing the motor to run hot? Maybe something is causing ozone.
I mean, if a properly installed CO2 scrubber normally bumps up pH but is instead decreasing pH, with recirculating compounding the problem, this can’t logically be probe errors. The probe doesn’t change. Something is changing. The media somehow leaching in would force pH up too high, so that can’t be it. What then are the variables? Flow maybe. CO2 should be reducing. If CO2 is reduced, is there some reason why in some skimmers that might affect bubble size? Perhaps not enough to make any sense. But then why is this happening?
 

LuisPerez711

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The below is a very informative read. Deals with all the issues or scenarios mentioned above.

A CO2 scrubber worked for me. Gave me a .1 boost and kept levels pretty stable. I think we sometimes have to be realistic on the outcome a certain product produces. I have read some threads that praise CO2 scrubbing, showing a .5 increase overnight but it's not the average. A .1 to .2 increase in ph seems to be the going rate for a CO2 scrubber.

 
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Randy Holmes-Farley

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I have been monitoring pH for some time, and the effects that I am noticing seem fairly certain. There seems to be some shared experience from others in this regard, inconsistent with others. The bubble size impact seems to have been studied, per my link, and is real. So, maybe there’s a different cause. If the phenomenon is real, there might be a fix.

Suppose it’s as simple as the specific model of skimmer and the motor type having to run slightly different due to back pressure from the tubing, scrubber, and recirculating all forcing the motor to run hot? Maybe something is causing ozone.
I mean, if a properly installed CO2 scrubber normally bumps up pH but is instead decreasing pH, with recirculating compounding the problem, this can’t logically be probe errors. The probe doesn’t change. Something is changing. The media somehow leaching in would force pH up too high, so that can’t be it. What then are the variables? Flow maybe. CO2 should be reducing. If CO2 is reduced, is there some reason why in some skimmers that might affect bubble size? Perhaps not enough to make any sense. But then why is this happening?

Certainly, there can be big differences in how well different skimmers aerate and exchange O2 and CO2.

Skimmers can raise or lower pH in different systems or at different times of the day in the same tank. There's no magic or mystery. It all exactly relates to whether there is more or less CO2 in the water than there would be in equilibrium with the air.

The bubble size effect on partial pressure has been known for a very long time, and is real, and is VERY small. It is smaller than the effect of depth/pressure, and far smaller than the effect of a properly operating scrubber on CO2.

I think you be exaggerating the effect of bubble size for bubbles normally present in a skimmer (not nanobubbles).

Please show us where in your link there is a substantial effect of bubble size on CO2 equilibration.

Let's look at the effects I see in the paper:

" Either the hydrostatic pressure at depth greater than 0.1 m or the surfacetension of bubbles smaller than 140 um is sufficient to counteract the 1% supersaturated dissolved gas pressure."


OK, so two big issues. First is that the increased pressure at a depth of 4 inches is equated to the bubble size effect for bubbles smaller than 0.14 mm. IMO, the depth effect may be more significant to a reef tank skimmer than is the bubble size.

Second, they are talking about offsetting a 1% increase in saturation. Might be important for scientists to study, but it is small in terms of pH.

1% supersaturation in CO2 would only cause a pH lowering of about 0.004 pH units. So the difference, say, between 8.050 and 8.046. No reefer is even measuring pH that accurately.
 

MnFish1

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A skimmer increases tank aeration and pushes pH towards equilibrium with the air intake CO2 regardless of bubble size and O2. Skimmer air is probably as clean as your indoor air and wouldn't impact anything.
You're much more adept at the pH chemistry in a reef tank that I am - but - I disagree with this statement. First - At least in my skimmer, there is a ton of 'stuff' on the wall of the skimmer cup (I do not clean it every day) - second - there is water at the bottom of the cup. Those areas are certainly not 'sterile' - i.e. there are tons of bacteria. And IMHO - won't those bacteria be converting O2 to CO2 and other things? If you smell your CO2 cup - does it smell like the air in your house? (Mine does not lol) - so - I believe that the recirculating system indeed would lower O2 levels - and probably add other chemicals to the water that are not removed by the CO2 scrubber. For example - My skimmer cup at times smells like H2S - is that being added back into the tank? etc etc.
 

arking_mark

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You're much more adept at the pH chemistry in a reef tank that I am - but - I disagree with this statement. First - At least in my skimmer, there is a ton of 'stuff' on the wall of the skimmer cup (I do not clean it every day) - second - there is water at the bottom of the cup. Those areas are certainly not 'sterile' - i.e. there are tons of bacteria. And IMHO - won't those bacteria be converting O2 to CO2 and other things? If you smell your CO2 cup - does it smell like the air in your house? (Mine does not lol) - so - I believe that the recirculating system indeed would lower O2 levels - and probably add other chemicals to the water that are not removed by the CO2 scrubber. For example - My skimmer cup at times smells like H2S - is that being added back into the tank? etc etc.

My skimmer is the same with crud and smell...recirculation has increased my CO2 media's life.
 

MnFish1

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My skimmer is the same with crud and smell...recirculation has increased my CO2 media's life.
That I believe - but that wasn't the question - the question was as I believe @Randy Holmes-Farley stated - could there be other detrimental effects. I.e. if the air going into the skimmer is so important with CO2, why not with other gases as well? I'm not asking just to argue - I recently got a new skimmer - and I was thinking about the issue of having all the waste (some of which was touching the 'foam' in teh cone of the skimmer, and my waste container is inside my closed sump. I wondered if the gasses produced were more detrimental. I can't help but think they are - and it led me to decide to clean my skimmer more.
 

arking_mark

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That I believe - but that wasn't the question - the question was as I believe @Randy Holmes-Farley stated - could there be other detrimental effects. I.e. if the air going into the skimmer is so important with CO2, why not with other gases as well? I'm not asking just to argue - I recently got a new skimmer - and I was thinking about the issue of having all the waste (some of which was touching the 'foam' in teh cone of the skimmer, and my waste container is inside my closed sump. I wondered if the gasses produced were more detrimental. I can't help but think they are - and it led me to decide to clean my skimmer more.

A couple thoughts here:
The chemical/elemental composition of skimmate generated by an H&S 200-1260 skimmer on a 175-gallon reef tank over the course of several days or a week had some surprises. Only a minor amount of the skimmate (solid + liquid) could be attributed to organic carbon (TOC); about 29%, and most of that material was not water soluble, i.e., was not dissolved organic carbon. The majority of the recovered skimmate solid, apart from the commons ions of seawater, was CaCO3, MgCO3, and SiO2 – inorganic compounds! The origin of these species is not known with certainity, but a good case can be made that the SiO2 stems from the shells of diatoms. The CaCO3 might be derived from other planktonic microbes bearing calcium carbonate shells, or might come from calcium reactor effluent. To the extent that the solid skimmate consists of microflora, then some proportion of the insoluble organic material removed by skimming would then simply be the organic components (the “guts”) of these microflora. These microflora do concentrate P, N, and C nutrients from the water column, and so their removal via skimming does constitute a means of nutrient export.
  • If we agree with above, only 29% of the skimmate is TOC and the rest would have no impact. The origin of this skimmate are microflora and some accumulated junk (food/poop). I don't believe that touching this stuff with the foam would provide significant contribution back to tank. At worst it would just provide a slight increase in nutrients.
  • Now what about recirculating the smelly air? More then likely, the skimmate becomes smelly as it becomes stagnant and promotes anaerobic digestion that can result in hydrogen sulfide gas. If you are cleaning you skimmer more frequently this is less likely to happen. Maybe @Randy Holmes-Farley can provide some insight on what the solubility of Hydrogen Sulfide gas would potentially have if recirculated though a skimmer.
 

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