CO2 scrubber

[tmz]

Anyone else locally using one of these?

I just got an order of medical grade soda lime ( calcium hydroxide 76%, sodium hydroxide 4% ,water 19 % from Airgas.
$90 for 5 gallons which should take care of my 600 g system for over a year.
It is used by divers and medical patients who need the air they breathe purged of CO2.

For years there have been many questions about controlling excess CO2 with solutions ranging from open windows, open water with surface agitation , opposite photoperiod chaeto refugia, limewater dosing , piping in outside fresh air and so on. All of which can help. But it's always nice to have another tool,particularly one that seems so promising in terms of effectiveness.

I read about CO2 scrubbers on the Chemistry Forum. Some are now selling devices commercially and calling them CO2 arrestors. The idea is to pass air going to the skimmer air intake through a chamber where the CO2 from the incoming air is chemically removed.
One approach is to bubble it through limewater /kalkwasser). Unfortunately the limewater uses up it's oxide quickly,preciptates, and stops taking up CO2.
Another is to pass it through a chamber containing dry calcium hydroxide(kalk powder) but the powder will restrict skimmer airflow and simply letting the air pass over it limits it's effectiveness without frequently shaking it up.
The soda lime comes in granular form about the size of crushed coral pieces. It is designed for breathing apparatus and offers little to no air flow restriction. The commercial name for it is sofnolime. It has nice feature in that it changes from white to purple when it's exhausted.

I simply took a one gallon jug with a large cap and cut slits in the bottom with a dremmel wheel and glued on some feet( small pieces of egg crate) to allolw air to pass under the jug. Then I took a piece of hose that fit over my skimmer air intake hose; cut a hole to match it in the cap for the jug ; pushed the hose in and sealed it on the outside of the cap with some Plumber's goop. Done.

I added about a liter of soda lime to the jug and plugged in my skimmer air intake hose. Runs nice and quiet and there is no apparent air flow restriction.

I'll be tacking ph over the next couple of weeks to see how well it performs. Some who have used it have reported consistent bumps in ph by .2 to .4 units. eg from 8.0 to 8.2/.3 or even .4.

The idea is simple. This media absorbs the CO2 ,so the air bubbling in through the skimmer has none with an overall effect of reducing transient CO2 in the water which rasies the ph. The oxide in the calcium hydroxide and the sodium hydroxide link with the CO2 and form carbonate on the media which has enough moisture in it to facilitate the process.

 

[redrider911]

Subscribed. I would like to know if there is a formula of gal of water to liters of soda lime to amount of days so that we can figure out how much a soda lime 90 gal tank would go through in a month. That way people with smaller tanks might be interested in doing a group buy to help with the costs. That .2 to .4 may still not be enough for people experiencing very low ph but I think it will cover most peoples' issues. Keep us posted Tom.

 

[tmz]

I put in a liter for my 600g system and will track when it is used up along with any ph bump. So with some math we should be able to approximate usage rates for various size tanks.I think some specifics will be obvious in about a month.

 

[Dave VG]

Subscribed as well. So where did you get the soda lime? Oh and a picture would be nice Tom.

Thanks

 

[tmz]

Yeah I'll do a picture. Not much to see. Just an empty 1 gallon BRS gfo jug with holes in the bottom and the top with a piece of hose popped through the top. Airgas has the soda lime sofnolime. They have stores throughout the country with an on line locator. I got mine in their store in Cheektowaga.

 

[mr.maroonsalty]

I'm curious how quickly it will help raise pH; do you think a pump connected to a controller pulling/pushing air through the material to a stone would have any short term effect?

 

[Dave VG]

Got ya no pic needed i thought it was more elaborate than that guess i should have read it better. Thanks

 

[tmz]

I'm curious how quickly it will help raise pH; do you think a pump connected to a controller pulling/pushing air through the material to a stone would have any short term effect?


Probably some. The skimmer is just a big bubbler.
One fellow in one of the other threads on CO2 scrubbers added a tee to the line feeding the skimmer to mix in some untreated air in amounts controlled by a ball valve in an effort to regulate ph rises.It would be neat tho have the whole thing work on a controller to a preset ph max but that would preclude using it on a 24/7 skimmer.

I think the overall rise will depend on how much volume the skimmer moves through it vis a vis the size of the system and variables such as the amount of open water facillitating air exchange with the air around the tank, levels of CO2 in the surrounding air etc. In my case I have 2 skimmers. One moves 1500g per hour through it; the other 900 g . I have started the CO2 scrubber on the larger one and left the other to pull air from the room. I may add a scrubber to that one later.

 

[toddmh]

Subscribed also..

Tom I am not great at this water chemistry stuff yet..But I seem to remember something Randy Holmes was writing about mixing white vinegar in your kalk solution to do something about the Co2..

Is this a different way of scrubbing Co2,and will this affect the alk or Ca in the system..?? I need to go take a chemistry coarse or something lol I stink at it..

 

[mr.maroonsalty]

Vinegar allows you get more lime into solution by increasing the saturation limit, and/or it reduces the pH of the solution. Its good if you can use more Alk and Ca than 2 tsps per gallon yields, or you need to lower the ph addition of your limewater, but you have to know you are also dosing a carbon source entailing all its implications.

 

[tmz]

Todd,
No it won't affect calcium and alkalinity levels in any direct way since none of the soda lime goes into the water, only the relatively CO2 free air goes to the skimmer air intake. The CO2 is trapped by the oxides in the soda lime. This lowers the level of CO2 in the water compared to a skimmer bubbling in room air with CO2 in it. Less CO2 in the water ,lessens the amount of carbonic acid( H2CO3) formed by some of the CO2 which hydrolizes in water. Less carbonic acid means less H protons which means higher ph. Excess CO2 in the water lowers ph.

White vinegar is a 5% solution of acetic acid(CH3 OOH) which as it breaks down to acetate and hydronium adds H protons to the water lowering the ph which allows more calcium hydroxide to remain in solution For example folks who want to dose more than 2 tsps per gallon can go up to 2.72 tsps per gallon by adding 48ml vinegar per gallon of mixing water . Vinegar also provides an organic carbon source which fuels bacterial growth and possible blooms . For this reason it is generally recommended that anyone spiking limewater with vinegar start at no more than 12 ml per gallon which would only allow an increase in calcium hydroxide to 2.18 tsps per gallon without precipitation.

Limewater is calcium hydroxide(Ca(OH)2 which in water disassociates to Ca(calcium) and oxide. The Hdroxide(O) joins up with CO2 forming CO3(carbonate). Some of the carbonate picks up H+ protons to form HCO3(bi carbonate) . The ratio of carbonate to bicarbonate varies in relation to ph( which is a measure of the number of H protons in the water; more H = lower ph)) . At lower ph there is more bi carbonate since there are more available H protons.So, when you dose limewater(kalk) you create carbonatesome of which transforms to bicarbonte by taking up an H proton.This loers the number of H protons in the water thus raisng the ph . You also deplete CO2 as it is used to form CO3( carbonate) , this also raises ph since there is less CO2 to form carbonic acid( H2 CO3) which is formed when CO2 hydrolizes( CO2 + H2O--> H2CO3).

 

[dreaminmel]

Less CO2 in the water, lessens the amount of carbonic acid( H2CO3) formed by some of the CO2 which hydrolizes in water. Less carbonic acid means less H protons which means higher ph. Excess CO2 in the water lowers ph.

Tom, Are there any other benefits to using it or is it strictly related to CO2? My pH runs at 8.3-4 consistently but because some of this chemistry stuff still escapes me, I thought I should double check. It used to run lower over a year ago so I stocked up on the 2part Alk that raises pH and now have to dose carefully to keep it from going higher. Haven't actually dosed in over a month and pH isn't going down.

 

[der_wille_zur_macht]

Tom, Are there any other benefits to using it or is it strictly related to CO2? My pH runs at 8.3-4 consistently but because some of this chemistry stuff still escapes me, I thought I should double check. It used to run lower over a year ago so I stocked up on the 2part Alk that raises pH and now have to dose carefully to keep it from going higher. Haven't actually dosed in over a month and pH isn't going down.

Don't mean to butt in on Tom's thread, but no - there will be no other benefits. The only people who would benefit from a CO2 scrubber would be people who can't keep their pH high enough through other means.

IMHO pH is over-complicated by people in this hobby. Someone with a more formal chemistry background will shoot me for this, but think of it as a ratio between CO2 and alkalinity. You can change the pH by altering either side of the ratio.

Every reef tank should be maintained to a specific alkalinity. So, in essence, that side of the ratio should be fixed. If you are doing a good job at maintaining alkalinity, and you still have "pH problems," it essentially means you have a CO2 problem. If you can't or don't want to solve it by the methods Tom mentioned in his first post (bringing in outside air, reverse photoperiods on a macroalgae refugium or turf scrubber, etc.) then a CO2 scrubber is a great solution. If you don't have pH problems, and your alkalinity is in line, then a scrubber won't help your tank.

 

[tmz]

No Melaniee, there are no other benefits to a CO2 scrubber . All that happens is that CO2 scrubbed air is pulled in by the sump instead of room air. If your ph is high there is no need for a CO2 scrubber.

Your ph sounds fine btw. The BRS product are using is baked baking soda or CO3(carbonate). It raises alkalinity and ph since it adds to carbonate alkalinity and as carbonate some of it will take of H+ as it transforms to bicarbonate and it will reduce H + in the water as a result.
My ph ran 8.2 to 8.35 for years. After dosing vodka and vinegar for 20 months for the organic carbon source to grow and feed nitrate/phosphate reducing bacteria, it has slowly dropped into the 7.9 to 8.15 range daily even though I continued to dose limewater. Bacterial activity generates some acid and CO2.
Ph above 7.8 is ok and mine(7.95 to 8.15)is pretty good , arguably optimal, but I'd like to add another point or two without increasing alkainity and I think the scrubber can help with that.NSW is usually cited at 8.2 but some reefs swing from 8.0 to 8.6
How are you measuring ph? FYI, Kits are tough and monitors tend to drift upward when in need of recalibration.

 

[dreaminmel]

Thank you Dwzm and Tom for the explanations. Makes perfect sense.

Tom, Back when my pH ran lower I was dosing vodka so that additional info make it click even more for me. I measure pH using a Pinpoint monitor that is calibrated once a month, sometimes every other. The probe was replaced last year after it went bad.

 

[toddmh]

yes guys..Good job with the explanations,I'm starting to grip this stuff lol I think

 

[tmz]

IMHO pH is over-complicated by people in this hobby. Someone with a more formal chemistry background will shoot me for this, but think of it as a ratio between CO2 and alkalinity. You can change the pH by altering either side of the ratio.

Every reef tank should be maintained to a specific alkalinity. So, in essence, that side of the ratio should be fixed. If you are doing a good job at maintaining alkalinity, and you still have "pH problems," it essentially means you have a CO2 problem.

I agree,excess CO2 depresses ph and thinking of it as a ratio between CO2 and alkalinty is a good way to go.U
Understanding how CO2 adds to H is optional.
Keeping alkalinity constant is very important particularly so with more sensitive corals like sps, in my experience. More so than ph as long as ph remains in an acceptable range( 7.8 to 8.5) So, using alkalinity supplements to manage ph is a poor way to do it since they add alkalinity and any bump in ph may be short lived effect since CO2 flows back in with the air and biological processes.
A scrubber does not effect alkalinity and provides air with low CO2 continuously.

Maintaining higher ph may lower alkalinity to some extent since both biotic( skeletal growth) and abiotic( white solids on heaters pumps etc.)precipitation occur more easily at higher ph resulting in more carbonate alkalinity being used over time.

 

[der_wille_zur_macht]

Keeping alkalinity constant is very important particularly so with more sensitive corals like sps, in my experience. More so than ph as long as ph remains in an acceptable range( 7.8 to 8.5) So, using alkalinity supplements to manage ph is a poor way to do it since they add alkalinity and any bump in ph may be short lived effect since CO2 flows back in with the air and biological processes.

Here here!

Continuing on the soapbox, IMHO it is often the case that people unknowingly focus on pH as a surrogate for alkalinity, when they should just forget about pH and focus on alkalinity. Monitor pH as a secondary parameter. Proceed with caution if you are about to alter a working alkalinity maintenance regimen in attempt to solve a pH problem. Instead, nail your alkalinity regimen, then think about CO2 if your pH is out of whack as a result.

That's my approach at least, interested to hear from others if they have another take on the subject.

 

[Gravesj1s]

I agree guys.

Glad this thread was started and folks are chiming in.I haven't really had a chance to get over to the chemistry forum yet to check the threads over there but got the gist to how this works from the discussion so far.
But I'd also point out that some alkalinity supplements are "questionable".I'm not up to par on all of whats out there these days but I know the seachem products add borates to the mix.It claims to maintain Ph.I believe this comes at a cost to carbonate alkalinity. Personaly I'd never use their alkalinity supplements for this reason.
In other words,adding this type product can shift Ph towards 8.3 while a alkalinity test kit "might read" this giving the illusion alkalinity is in the acceptable range.Borate is part of what makes up Alk,but not really used in calcification.

Another thing to consider would be growth.Ph ranging between 7.9 -8.5 are considered the "acceptable ranges",but the optimum range for calcification is towards the upper limits.I believe Ph 8.4 growth rates are maximized.Something to consider if they were using a Caco3 reactor whitch is known for lower but in the acceptable Ph range.

I do agree though that maintaining alk is more important than worrying about Ph numbers.I do monitor Ph but it is more for cautionary measures (limewater) than anything else.

 

[toddmh]

Here here!

Continuing on the soapbox, IMHO it is often the case that people unknowingly focus on pH as a surrogate for alkalinity, when they should just forget about pH and focus on alkalinity. Monitor pH as a secondary parameter. Proceed with caution if you are about to alter a working alkalinity maintenance regimen in attempt to solve a pH problem. Instead, nail your alkalinity regimen, then think about CO2 if your pH is out of whack as a result.

That's my approach at least, interested to hear from others if they have another take on the subject.

guilty here lol :fun5: This was me till a few weeks ago,now that my alk levels are pretty stable..I noticed that my Ph is falling in line on it's own