How exactly does CO2 Scrubbing impact reef chemistry?

george9 · Jun 27, 2023

Hi all,
It’s time I implement some type of co2 scrubbing procedure as my chronically low pH is getting to me. Tested around 7.7 yesterday afternoon right after lights ramped up and this is just a tad low for my liking. Took a cup of tank water outside and let it sit for an hour (didn’t even oxygenate it) and the pH bounced up to 8.0-8.1 so i’m certain this is Co2. Nearing the end of the photoperiod, I barely am making it to 8.0 on most days, maybe reaching 8.1 on good days.

This is for a Biocube, so just using a simple BRS chamber with soda lime and an air pump with an air stone in the back chamber to effectively oxygenate the water with Low Co2 air and subsequently increase the pH.

My concerns are with the chemistry of this addition. My tank is pretty stable, and I am
concerned installing this could completely throw everything out of wack and crash the tank. Am I overthinking here?

How does a pH increase impact the big 3 - Ca, mg and alk? I understand I’ll have to re-balance my dosing as alk usage will skyrocket with a higher pH, but could there be any other detrimental chemistry effects that I am not aware of? I use All for Reef to supplement Ca, mg and Alk at the moment and am hoping increasing my dosage will continue to maintain everything properly.
can a pH swing after the addition of the scrubber cause RTN? When first installed, how closely should I be watching Ph? Say my pH swings from 7.7 to 8.1 after I begin scrubbing, will this sort of swing cause RTN in SPS? I highly doubt I’ll be able to get much above 8.2 with how low I already run in this high co2 environment.

Also anything else to keep an eye on parameter-wise after the scrubber is installed? I want to cover all my bases here and prevent a disaster.

thank you, any input is appreciated!

Randy Holmes-Farley · Jun 27, 2023

george9 said:
Hi all,
It’s time I implement some type of co2 scrubbing procedure as my chronically low pH is getting to me. Tested around 7.7 yesterday afternoon right after lights ramped up and this is just a tad low for my liking. Took a cup of tank water outside and let it sit for an hour (didn’t even oxygenate it) and the pH bounced up to 8.0-8.1 so i’m certain this is Co2. Nearing the end of the photoperiod, I barely am making it to 8.0 on most days, maybe reaching 8.1 on good days.

This is for a Biocube, so just using a simple BRS chamber with soda lime and an air pump with an air stone in the back chamber to effectively oxygenate the water with Low Co2 air and subsequently increase the pH.

My concerns are with the chemistry of this addition. My tank is pretty stable, and I am
concerned installing this could completely throw everything out of wack and crash the tank. Am I overthinking here?

How does a pH increase impact the big 3 - Ca, mg and alk? I understand I’ll have to re-balance my dosing as alk usage will skyrocket with a higher pH, but could there be any other detrimental chemistry effects that I am not aware of? I use All for Reef to supplement Ca, mg and Alk at the moment and am hoping increasing my dosage will continue to maintain everything properly.
can a pH swing after the addition of the scrubber cause RTN? When first installed, how closely should I be watching Ph? Say my pH swings from 7.7 to 8.1 after I begin scrubbing, will this sort of swing cause RTN in SPS? I highly doubt I’ll be able to get much above 8.2 with how low I already run in this high co2 environment.

Also anything else to keep an eye on parameter-wise after the scrubber is installed? I want to cover all my bases here and prevent a disaster.

thank you, any input is appreciated!

A CO2 scrubber raises pH and doesn’t do anything else that would not be the case if you were naturally at that pH.

george9 · Jun 27, 2023

Randy Holmes-Farley said:
A CO2 scrubber raises pH and doesn’t do anything else that would not be the case if you were naturally at that pH.

Thanks Randy

I hear “don’t chase pH” for fear of causing instability so much that I just wanted to clear it up.

Any instabilities some may experience from chasing pH would likely just be due to increased growth at a higher pH then?

Randy Holmes-Farley · Jun 27, 2023

george9 said:
Thanks Randy

I hear “don’t chase pH” for fear of causing instability so much that I just wanted to clear it up.

Any instabilities some may experience from chasing pH would likely just be due to increased growth at a higher pH then?

I have never once told someone to not chase pH. There is absolutely nothing wrong with trying to adjust or control ph.

The issue is what you do to adjust pH.

If you approach it correctly, there is no going to be a problem.

If you approach it incorrectly, then there can be issues, just as applies to almost anything else a reefer does.

The issue is not helped by bogus claims by manufacturers that you can boost pH and not alk by adding their products. Or that using their additive will give pH 8.35 or some such fever dream comment. Fail. They all boost alk, and excessive alk is a primary problem with adding stuff to boost pH.

Court_Appointed_Hypeman · Jun 27, 2023

george9 said:
Thanks Randy

I hear “don’t chase pH” for fear of causing instability so much that I just wanted to clear it up.

Any instabilities some may experience from chasing pH would likely just be due to increased growth at a higher pH then?

Chasing PH to my understanding refers to people attenpting to raise PH using products that ate actually adding alkalinity, as there is no real chemical additive that can achieve removal of co2 without raising DKH... if its going into the water.

CO2 scrubbing while chemical, is not going into the water and will achieve a reduction of the introduction of CO2 into the system, raising PH.

One affect that it can have as a nefative is reduced O2 IF you recirculate your only skimmer with the scrubber and you have no other gas exchange such as turbulant water surfaces.

I recirculate my scrubber, but have a lot of surface turbulance, which does reduce the effectiveness of the scrubber a little since co2 can be reintroduced at the surface of the water, but it is less introduction than my skimmer alone with no scrubber so its a net gain in PH, and probably a slight reduction of O2 introduction.

george9 · Jun 27, 2023

Randy Holmes-Farley said:
I have never once told someone to not chase pH. There is absolutely nothing wrong with trying to adjust or control ph.

The issue is what you do to adjust pH.

If you approach it correctly, there is no going to be a problem.

If you approach it incorrectly, then there can be issues, just as applies to almost anything else a reefer does.

The issue is not helped by bogus claims by manufacturers that you can boost pH and not alk by adding their products. Or that using their additive will give pH 8.35 or some such fever dream comment. Fail. They all boost alk, and excessive alk is a primary problem with adding stuff to boost pH.

Court_Appointed_Hypeman said:
Chasing PH to my understanding refers to people attenpting to raise PH using products that ate actually adding alkalinity, as there is no real chemical additive that can achieve removal of co2 without raising DKH... if its going into the water.

CO2 scrubbing while chemical, is not going into the water and will achieve a reduction of the introduction of CO2 into the system, raising PH.

One affect that it can have as a nefative is reduced O2 IF you recirculate your only skimmer with the scrubber and you have no other gas exchange such as turbulant water surfaces.

I recirculate my scrubber, but have a lot of surface turbulance, which does reduce the effectiveness of the scrubber a little since co2 can be reintroduced at the surface of the water, but it is less introduction than my skimmer alone with no scrubber so its a net gain in PH, and probably a slight reduction of O2 introduction.

Makes sense to me, thanks guys! Wasn’t saying I’ve seen posts from you specifically claiming to not chase pH, but more of a general sentiment I’ve seen on forums (including this one) from other reefers.

I am not planning on connecting this to my skimmer since I have the basic Biocube skimmer and not sure it sucks enough air to make a difference. I ordered a relatively large and tuneable air pump which I will use to pump co2-free (or greatly reduced) air into the back chamber to bump pH. I also have plenty of surface agitation so it will be interesting seeing how much I can bump pH up with this system given that the skimmer and agitation will be working against the scrubber. I know it surely won’t reduce pH so it’s worth a shot .

jda · Jun 27, 2023

I tell people to just keep alk stable and not chase pH unless you have a very good reason to do so, or really good at reefing... and assuming that your lows are not too much below 7.8. I have just seen too many bad things happen with crashes (alk raising and precipitating or kalk overdose, etc) and unintended consequences from people worrying too much. I have also never seen any issues with night pH of 6.8. This is probably splitting hairs, but most have more important things to worry about, IMO.

The best thing that you can do for your pH is to buy a indoor co2 monitor and make sure that your home has co2 levels in the 400-500 level, or at least below 700. Over 700 and the tank's pH can drop. There is nothing chemical about this at all and it can help the humans and pets in the home too. IME, this will do a safer and better job than any other method.

Check this thread out where dude now has stable pH with some simple changes:

I need to Revisit PH Again

My tank is a little over a year old now and very stable except for one thing. PH. Through a year of observation, I’m pretty sure the issue revolves around the CO2 level in the house. It’s a new house and very well sealed. Here’s the parameters. Tank plus sump is about 180 gallons. Temp...

www.reef2reef.com

Randy Holmes-Farley · Jun 27, 2023

george9 said:
Makes sense to me, thanks guys! Wasn’t saying I’ve seen posts from you specifically claiming to not chase pH, but more of a general sentiment I’ve seen on forums (including this one) from other reefers.

I am not planning on connecting this to my skimmer since I have the basic Biocube skimmer and not sure it sucks enough air to make a difference. I ordered a relatively large and tuneable air pump which I will use to pump co2-free (or greatly reduced) air into the back chamber to bump pH. I also have plenty of surface agitation so it will be interesting seeing how much I can bump pH up with this system given that the skimmer and agitation will be working against the scrubber. I know it surely won’t reduce pH so it’s worth a shot .

Sounds like a fine plan to me.

george9 · Jun 27, 2023

jda said:
I tell people to just keep alk stable and not chase pH unless you have a very good reason to do so, or really good at reefing... and assuming that your lows are not too much below 7.8. I have just seen too many bad things happen with crashes (alk raising and precipitating or kalk overdose, etc) and unintended consequences from people worrying too much. I have also never seen any issues with night pH of 6.8. This is probably splitting hairs, but most have more important things to worry about, IMO.

The best thing that you can do for your pH is to buy a indoor co2 monitor and make sure that your home has co2 levels in the 400-500 level, or at least below 700. Over 700 and the tank's pH can drop. There is nothing chemical about this at all and it can help the humans and pets in the home too. IME, this will do a safer and better job than any other method.

Check this thread out where dude now has stable pH with some simple changes:

I need to Revisit PH Again

My tank is a little over a year old now and very stable except for one thing. PH. Through a year of observation, I’m pretty sure the issue revolves around the CO2 level in the house. It’s a new house and very well sealed. Here’s the parameters. Tank plus sump is about 180 gallons. Temp...

www.reef2reef.com

Those sort of alk swings is what I am worried about but since I have not automated dosing, this can easily be mitigated because I always test alk before I dose daily and can adjust the daily hit of AFR as needed. If my dosing was automated, I’d be worried about really bad alk swings as consumption changes when media gets used up or is replaced. In that case, I probably would just let pH be out of fears the automation in dosing will cause an issue.

I am trying this out because my growth when I am home is no where near where it is when I am away, which points to a Co2 issue. I left for 5 days and my alk plummeted with the increased pH due to lower co2 in the apartment. I have not measured exactly but I will tell you I live in a 1bedroom apartment in Florida, sealed with AC most of the year with 2 people and 3 dogs and often many visitors. My co2 has to be above 1000 lol

Tank looks great, corals grow just okay, I have a couple montis that haven’t really flourished but also not died. Recently some zoas are randomly ticked and I am not sure why. Acros do okay, coralline algae is lacking. It grows super slowly but eventually gets kinda thin, I bet higher pH would help this (although I may regret that aspect when it grows out of control lol)

Randy Holmes-Farley · Jun 28, 2023

FWIW, the alk swings you are worrying about may also be happening just by having more people around one day, or more cooking with gas appliances.

george9 · Jun 28, 2023

Randy Holmes-Farley said:
FWIW, the alk swings you are worrying about may also be happening just by having more people around one day, or more cooking with gas appliances.

I’ve noticed small differences in alk usage due to this when I test daily although nothing like when everyone vacated the apartment for 5 days and the alk plummeted from 8.2 to 6.7 with the typical dosing regimen when Co2 is elevated.

pH was 7.6 this morning before lights came on and I did have extra people over last night. If I am only able to just pad those nightly lows up to 7.8 with this scrubber I will be happy. I don’t mind topping out at 8.0 as long as I don’t dip below 7.8 at night.

Court_Appointed_Hypeman · Jun 28, 2023

george9 said:
I’ve noticed small differences in alk usage due to this when I test daily although nothing like when everyone vacated the apartment for 5 days and the alk plummeted from 8.2 to 6.7 with the typical dosing regimen when Co2 is elevated.

pH was 7.6 this morning before lights came on and I did have extra people over last night. If I am only able to just pad those nightly lows up to 7.8 with this scrubber I will be happy. I don’t mind topping out at 8.0 as long as I don’t dip below 7.8 at night.

We have a full house with pretty high CO2 my scrubber keeps it at minimum 8.02 (according to a probe which may be accurate on how much the value changes, but may be inacurate on the specific value)

If you are planning on running it on something other than your skimmer, it may not have much of am affect because the skimmer is going to be responsible for putting it in equilibrium with the air in your house. I am not sure connecting it to an aireator will do much since the airator causes gas exchange via the turbulamce it causes and not from the air that it pumps in.

george9 · Jun 28, 2023

Court_Appointed_Hypeman said:
We have a full house with pretty high CO2 my scrubber keeps it at minimum 8.02 (according to a probe which may be accurate on how much the value changes, but may be inacurate on the specific value)

If you are planning on running it on something other than your skimmer, it may not have much of am affect because the skimmer is going to be responsible for putting it in equilibrium with the air in your house. I am not sure connecting it to an aireator will do much since the airator causes gas exchange via the turbulamce it causes and not from the air that it pumps in.

That’s true. I run the Coralife Biocube skimmer on this tank which is pretty weak. I’m hoping since the air pump will be pushing significantly more air than the small skimmer, it won’t completely offset the pH bump from the air pump scrubber but likely won’t be quite as efficient as when the skimmer is off completely. I’ll have to see how it does for me when the parts arrive on Friday.

Perhaps I can only run the scrubber at night and turn off the skimmer while it’s running overnight to buffer the pH drop in the dark. Once the lights ramp up, the tank doesn’t have an huge issue climbing to around 8.0 so maybe I can leave the scrubber off when lights are on. Not sure yet - We’ll see what happens. Going to be some trial and error!

george9 · Jun 29, 2023

Once the scrubber is installed, is there any risk of coral damage by raising pH too quick? I have no idea how quickly or slowly this will begin to raise my pH but would there be an issue going from say around 7.6 to 8.2 in a few hours? I have SPS, LPS and softies in this tank

Randy Holmes-Farley · Jun 29, 2023

george9 said:
Once the scrubber is installed, is there any risk of coral damage by raising pH too quick? I have no idea how quickly or slowly this will begin to raise my pH but would there be an issue going from say around 7.6 to 8.2 in a few hours? I have SPS, LPS and softies in this tank

I do not believe so, unless nutrients are very low, in which case some chance of burnt tops on certain SPS corals, just like high alk and low nutrients can give burnt tips.

george9 · Jul 3, 2023

Well the scrubber has been pumping co2-reduced air into my back chamber since around 10PM on July 2. I did notice maybe a slight increase last night with the pH topping out around 8.1-8.2 which I am happy with. It did drop to around 7.6 again early this morning (and also yesterday morning) so I may need to make some tweaks. With my skimmer running 24/7 simultaneously pumping in co2-rich air alongside the airstone, they may be cancelling each other out as previously mentioned. With this being a biocube, I think the fact that it is covered is a good thing for the surface-atmosphere co2 exchange, but I may be wrong.

I am happy with my daytime pH once the lights kick on so I am thinking maybe only running the skimmer through the day until the lights shut off can help keep the pH up at night. My lights are on full blast from 1:30 to 9:30PM and ramp up beginning at 11:30AM and end the ramp down at 11:30PM. So maybe I can kick the skimmer off at 9:30 when pH is topped off and then the only aeration would be coming from the air stone with co2-reduced air and should hypothetically help bump that morning pH low up . I wouldn't lose the aeration-benefit of the skimmer at night since the airstone will be continuing through the night, and there won't be a source of high-co2 air anymore.

Before I do anything I want to let it do its thing for a couple more days. I am replicating the scrubber in this thread - https://www.reef2reef.com/threads/co2-scrubber-without-skimmer.918381/ and when they installed theirs, it took a good 4-5ish days to see maximum effect to pH according to their graph, so I may need a few more day-night cycles to get where I want.

I wish I can just install it to the skimmer air intake, but the stock intake has a little air valve on the end that controls the bubbling and if I had a skimmer on it, I'd lose this control and it likely wouldn't work well.

george9 · Jul 13, 2023

Well been about 10 days and happy to say this skimmerless Co2 scrubber has been working out very well albeit with a few minor annoyances.

With the scrubber as the only source of oxygenation at night (skimmer OFF), pH reaches a minimum of 7.9-8.0 in the AM now rather than 7.5-7.6. It tops out around 8.3 in the evening even with the protein skimmer pumping in co2 rich air during the day. I run the skimmer + scrubber simultaneously during the day and at night, the skimmer turns off for about 9 hours with only the scrubber working.

Alk usage has skyrocketed - basically more than doubled and growth has noticeably increased as well.

Annoying things:
-Media only lasted about 7-10 days my first time and is on track for another 7-10days with this new refill (changed 7/10) Going to play with the air flow to see if I can maximize this. I changed media 7/10 and already see light purple on the bottom 1/2 of it 4 days later.
- water at the bottom of the scrubber is SUPER important to the usefulness of the media IME. After changing the media and adding a bit of water, I am able to go around 3-4 days before the water dries up and the pH is able to dip in the mornings, leading to a small ( .3-.4dkh) alk spike. Once I add a bit of water again, the media scrubs co2 more efficiently and this isn’t an issue again until the water dries up or the media is used up. Since this is a skimmerless scrubber, I plan on getting a small plastic Sterilite container, filling it with about 1” of water and elevating the pump off the bottom of this closed container so the pump air intake is just above the surface of the water in this container. This *should* pump more humid air into the scrubber and hopefully with keep me from having to drop a few mLs of water into the bottom of the chamber itself. Having to open the chamber and add water every 3 days is too annoying.

george9 · Aug 1, 2023

Updating just in case someone stumbles on this thread down the road…

Putting the pump in a plastic container with water at the bottom has dramatically increased the length of time the media lasts (whoo hoo).

I was previously getting just a few days and now I’m pushing 10 days - 2 weeks depending on how high the CO2 is in the apartment.

I also purchased a cheap CO2 monitor (which likely is not accurate) but wanted to get a very general ballpark for what the levels in here look like. When I first turned it on, it showed 430ppm inside and slowly rose over the next few hours to 5000PPM!! It remains at 5000PPM unless the sliding glass door is wide open for 30-45minutes which is unbearable in Miami with 110 degree heat indices haha. Thinking this is way too high of a reading although it does appear to be accurate when taken outside (it shows 420ppm).
Regardless this confirms my pH issue was due to elevated CO2, and with this setup I rigged up, the pH has not dropped below 7.9 in the mornings.

My All For Reef dosage jumped from 3-4mL/day to about 10mL per day at the elevated pH.

All in all, this cheap little set up is a win if you are fighting extremely elevated CO2 in a small space like I am.