Tuning a Skimmer / CO2 Scrubber for pH Control

arking_mark

2500 Club Member
View Badges
Joined
Mar 2, 2016
Messages
2,592
Reaction score
1,814
Location
Potomac
Rating - 0%
0   0   0
On my reefing journey, I found Kalkwasse + Skimmer + CO2 Scrubber to be very effective for bringing my pH from 7.8 - 7.9 to 8.26 - 8.36.

I guess most people would just leave it at that. However, I wanted to be more efficient with the CO2 scrubbing material so I wanted to implement a recirculating CO2 scrubber and control the airflow through the media to the skimmer. So I upgraded to an Aeraqua Duo.

Please note, I am not really looking to use my skimmer for filtration. So the question is how to tune this for efficient pH control.

My basic understanding of skimmers (which may or may not be true):
1. Foam head needs to break at or above the collar (base of the cup)
2. For wetter skimmate raise the foam head
3. Needle wheel venturi generally perform best when air is appropriately restricted to the pump as this actually increases pump speed and air draw.

Controls on the skimmer:
1. Exit gate valve - closing the gate raises the water level in the skimmer
2. Pump speed - increases water and air draw
3. Left-right external/recirculation control - pulls mix of internal and external water

I added the following controls:
1. An air solenoid valve that can switch between CO2 scrubbed air and house rich CO2 air
2. An inline shut-off valve that I can manually adjust to restrict airflow (not sure this is needed because of #2 above)

So how do we optimize this for pH control? There are so many dials to adjust.

A couple of thoughts:
1. Setting it to DC motor speed to 100% maximizes air-water mixture and should maximize pH impact
2. Maximizing recirculation would then produce higher pH water exiting the skimmer
3. Minimizing recirculation would move more tank water through the skimmer
4. Would running the DC motor at 50% with some recirculation be better and help not over skim the tank
5. The air solenoid is set to maintain the pH at 8.35 with a .05 hysteresis
6. I'm not sure I need an airflow restricted with the DC pumps
7. I don't think 2 & 3 make much difference
8. I think I may be better off shutting off the skimmer instead of switching to unscrubbed air which will drive pH down

Thoughts?
 
Last edited:

Randy Holmes-Farley

Reef Chemist
View Badges
Joined
Sep 5, 2014
Messages
66,550
Reaction score
62,845
Location
Arlington, Massachusetts, United States
Rating - 0%
0   0   0
A couple of thoughts:
1. Setting it to DC motor speed to 100% maximizes air-water mixture and should maximize pH impact
2. Maximizing recirculation would then produce higher pH water exiting the skimmer
3. Minimizing recirculation would move more tank water through the skimmer
4. Would running the DC motor at 50% with some recirculation be better and help not over skim the tank
5. The air solenoid is set to maintain the pH at 8.35 with a .05 hysteresis
6. I'm not sure I need an airflow restricted with the DC pumps
7. I don't think 2 & 3 make much difference
8. I think I may be better off shutting off the skimmer instead of switching to unscrubbed air which will drive pH down

Thoughts?

#2/3. I do not think there is a rationale for wanting ANY recirculation of the water. Yes, recirculation of water raises the pH most/ removes CO2 most for a single pass through the skimmer, but a skimmer on a reef tank is not single pass device.

If the goal is to drive out CO2, it is always best to have lower pH/higher CO2 water in the skimmer to maximize the removal of CO2 (by maximizing the difference between the water and the air CO2 level). Hence, no water recirculation will export the most CO2 over time.
 
OP
OP
arking_mark

arking_mark

2500 Club Member
View Badges
Joined
Mar 2, 2016
Messages
2,592
Reaction score
1,814
Location
Potomac
Rating - 0%
0   0   0
#2/3. I do not think there is a rationale for wanting ANY recirculation of the water. Yes, recirculation of water raises the pH most/ removes CO2 most for a single pass through the skimmer, but a skimmer on a reef tank is not single pass device.

If the goal is to drive out CO2, it is always best to have lower pH/higher CO2 water in the skimmer to maximize the removal of CO2 (by maximizing the difference between the water and the air CO2 level). Hence, no water recirculation will export the most CO2 over time.

Thanks. So minimize recirculation it is.
 
OP
OP
arking_mark

arking_mark

2500 Club Member
View Badges
Joined
Mar 2, 2016
Messages
2,592
Reaction score
1,814
Location
Potomac
Rating - 0%
0   0   0
Other than my solenoid valve being down, I am able to maintain pH within 8.325 and 8.375 (8.35 setpoint w/ .05 hysteresis) by manually switching between house air and CO2 scrubbed air.

I've actually left the skimmer set for Maxpects recommendations for skimming my size tank/bioload which is 80%/0% right/left external circulation, 80% power, and gate adjusted to skimmate preference (I went wet since it on intermittently). Per their recommendations, an airflow restrictor isn't needed.
 
OP
OP
arking_mark

arking_mark

2500 Club Member
View Badges
Joined
Mar 2, 2016
Messages
2,592
Reaction score
1,814
Location
Potomac
Rating - 0%
0   0   0
@Randy Holmes-Farley

Other than having fun dialing in my system parameters. Is there any known benefit to locking in pH in a tight range as I have? Or is this just total overkill?

With this beast of a skimmer, I am able to quickly drive up or down pH. I'll try to get some numbers, but with a 3ml/min Kalk drip and the dynamic nature of the tank, I'm not sure what they will really mean.

After hooking up the skimmer, before I knew it, the pH went from 8.31 to 8.53 in 9hrs (~0.024 pH/hr). Then I removed the CO2 scrubber and was surprised again when the pH went from 8.53 to 8.30 in 4hrs (~0.058 pH/hr)

I'm sure there is a chemistry explanation why it was about twice as easy to drive down pH than drive it up, but I'll leave that to @Randy Holmes-Farley

2021-03-15 (3).png
 
OP
OP
arking_mark

arking_mark

2500 Club Member
View Badges
Joined
Mar 2, 2016
Messages
2,592
Reaction score
1,814
Location
Potomac
Rating - 0%
0   0   0
BLUE arrow indicates when I switched up skimmers. RED arrow indicates when I started to use the skimmer to help regulate pH in the tank.

2021-03-19 (2)_LI.jpg

There are a couple of things to note:
  • Very effective at maintaining my pH within a 0.05 range (8.32 low and 8.37 high)
  • For me, I believe kalkwasser is providing the majority of the daily pH boost. My Kalk reactor turns off 4 times a day to mix and settle the Kalk (1hr). Almost always during this time, the skimmer will come on with the CO2 scrubber to boost the pH.
  • During peak lighting hours, the pH will go high enough (once or twice) for the skimmer to come on without the CO2 scrubber to lower the pH
  • On average, so far, the skimmer comes on roughly 3-6 times a day for about 1-2hrs each time. I'd estimate roughly 8hrs of skimming. Surprisingly, the skimmer output has remained roughly the same ~1/4 cup of dark tea skimmate
  • I haven't been able to find an affordable 3-way solenoid and will probably go with installing two regular solenoid valves in parallel. However, I'm really not sure the downregulation is needed as I'm not sure my pH will go above 8.37 without the skimmer and CO2 scrubber assisting. I'll find out this week as my skimmer will be off for the next 5 days.
 

Janci

Staghorns will prevail
View Badges
Joined
Mar 14, 2016
Messages
2,970
Reaction score
9,291
Location
Belgium
Rating - 0%
0   0   0
Interesting data you have found here.
It is a good call to switch off your skimmer instead of changing the air inlet to a more CO2 rich environment.
I also believe that this would make the pH fluctuation change faster and you will need more switching. It might however also make it possible to keep the pH in a smaller range. Maybe something to try?

I found this website a long time ago when I was working om my ATO/AWC system.
it might be of use for you.
https://www.electricsolenoidvalves.com/3-way-valves/ (They used to have 220V valves which are now discontinued)
 
OP
OP
arking_mark

arking_mark

2500 Club Member
View Badges
Joined
Mar 2, 2016
Messages
2,592
Reaction score
1,814
Location
Potomac
Rating - 0%
0   0   0
Interesting data you have found here.
It is a good call to switch off your skimmer instead of changing the air inlet to a more CO2 rich environment.
I also believe that this would make the pH fluctuation change faster and you will need more switching. It might however also make it possible to keep the pH in a smaller range. Maybe something to try?

I found this website a long time ago when I was working om my ATO/AWC system.
it might be of use for you.
https://www.electricsolenoidvalves.com/3-way-valves/ (They used to have 220V valves which are now discontinued)

Thanks! I'm not sure I need a 3-way anymore. I'll post some more recent findings soon.
 
OP
OP
arking_mark

arking_mark

2500 Club Member
View Badges
Joined
Mar 2, 2016
Messages
2,592
Reaction score
1,814
Location
Potomac
Rating - 0%
0   0   0
So just my final observations after weeks of excellent pH control.

For my setup, a solenoid wasn't needed. It turns on when pH drops and turns off when I hit my setpoint.

I highly recommend using a recirculating CO2 scrubber. It provides 3 benefits.
1. More effective at raising pH
2. More efficient use of media
3. You don't need to add water as the incoming Ir is damp for the media

One drawback with the higher pH has been abiotic precipitation of Calcium Carbonate. My tank is only 5 months old with a few frags. So actual coral Ca/Alk demand is low. The abiotic precipitation has manifested in clumping my sand. Pumps and other items do not seem to have buildup.
 

PeterC99

Solarbenchmark.com
View Badges
Joined
Aug 28, 2020
Messages
6,385
Reaction score
30,069
Location
White Plains, NY
Rating - 0%
0   0   0
So just my final observations after weeks of excellent pH control.

For my setup, a solenoid wasn't needed. It turns on when pH drops and turns off when I hit my setpoint.

I highly recommend using a recirculating CO2 scrubber. It provides 3 benefits.
1. More effective at raising pH
2. More efficient use of media
3. You don't need to add water as the incoming Ir is damp for the media

One drawback with the higher pH has been abiotic precipitation of Calcium Carbonate. My tank is only 5 months old with a few frags. So actual coral Ca/Alk demand is low. The abiotic precipitation has manifested in clumping my sand. Pumps and other items do not seem to have buildup.
I also put in a CO2 scrubber and I noticed the build up of calcium carbonate film on my UV quartz sleeve. Unfortunately a pain in the neck to clean.

Have a high demand Alk/Calc aquarium and was dosing 110ml of 2 part daily. Just switched to a calcium reactor and noticed after 3 weeks little build up on the UV quartz sleeve.

The high pH from CO2 Scrubber and high Alk/Calc from calcium reactor has really helped increase the grow of my corals!
 
OP
OP
arking_mark

arking_mark

2500 Club Member
View Badges
Joined
Mar 2, 2016
Messages
2,592
Reaction score
1,814
Location
Potomac
Rating - 0%
0   0   0
As I continue to monitor the tank pH and performance, what I have found is that the Kalkwasser does a very good job of maintaining the pH. Meaning, once the pH is at the target level Kalkwasser can maintain it for hours. When my tank pauses Kalkwasser for mixing (4x day), that's when the Skimmer/CO2 will deffinately kick on. Additionally, I don't see a pH drop off at night. In fact the refugium has been maintaining a higher pH then that of the day-time display tank. Again, this means that the CO2 scrubber kicks on less at night. I should also note, that I have no algae in the DT...but a ton of GHA in the sump along with some Chaeto and Calerpa.
 
OP
OP
arking_mark

arking_mark

2500 Club Member
View Badges
Joined
Mar 2, 2016
Messages
2,592
Reaction score
1,814
Location
Potomac
Rating - 0%
0   0   0
Just a quick update:

1. I'm maintaining target pH now at 8.3
2. I'm now seeing day/night pH swings as high as 8.27 to 8.34. Although it normally swings between 8.28 and 8.32. I believe this is due to a maturing tank (6 months old) with more CO2 consumers during the daylight hours.
3. Weekly Kalkwasser top-off
4. 6 week CO2 scrubbing media replacement
5. I've had a couple of issues with water blocking the recirculation tube.
6. I've had a couple issues with the Kalkwasser RODI water running dry...
 

Plandauesq

Active Member
View Badges
Joined
Jul 18, 2019
Messages
171
Reaction score
82
Rating - 0%
0   0   0
On my reefing journey, I found Kalkwasse + Skimmer + CO2 Scrubber to be very effective for bringing my pH from 7.8 - 7.9 to 8.26 - 8.36.

I guess most people would just leave it at that. However, I wanted to be more efficient with the CO2 scrubbing material so I wanted to implement a recirculating CO2 scrubber and control the airflow through the media to the skimmer. So I upgraded to an Aeraqua Duo.

Please note, I am not really looking to use my skimmer for filtration. So the question is how to tune this for efficient pH control.

My basic understanding of skimmers (which may or may not be true):
1. Foam head needs to break at or above the collar (base of the cup)
2. For wetter skimmate raise the foam head
3. Needle wheel venturi generally perform best when air is appropriately restricted to the pump as this actually increases pump speed and air draw.

Controls on the skimmer:
1. Exit gate valve - closing the gate raises the water level in the skimmer
2. Pump speed - increases water and air draw
3. Left-right external/recirculation control - pulls mix of internal and external water

I added the following controls:
1. An air solenoid valve that can switch between CO2 scrubbed air and house rich CO2 air
2. An inline shut-off valve that I can manually adjust to restrict airflow (not sure this is needed because of #2 above)

So how do we optimize this for pH control? There are so many dials to adjust.

A couple of thoughts:
1. Setting it to DC motor speed to 100% maximizes air-water mixture and should maximize pH impact
2. Maximizing recirculation would then produce higher pH water exiting the skimmer
3. Minimizing recirculation would move more tank water through the skimmer
4. Would running the DC motor at 50% with some recirculation be better and help not over skim the tank
5. The air solenoid is set to maintain the pH at 8.35 with a .05 hysteresis
6. I'm not sure I need an airflow restricted with the DC pumps
7. I don't think 2 & 3 make much difference
8. I think I may be better off shutting off the skimmer instead of switching to unscrubbed air which will drive pH down

Thoughts?
How large is the tank you have this skimmer on? I have a 300 gallon tank and considering buying a new skimmer to help boost my pH.
 

Randy Holmes-Farley

Reef Chemist
View Badges
Joined
Sep 5, 2014
Messages
66,550
Reaction score
62,845
Location
Arlington, Massachusetts, United States
Rating - 0%
0   0   0
How large is the tank you have this skimmer on? I have a 300 gallon tank and considering buying a new skimmer to help boost my pH.

A skimmer (or any type of aeration) will not boost pH if the room has elevated CO2 in the air. That is by far the most common cause of low pH in a reef tank.
 
OP
OP
arking_mark

arking_mark

2500 Club Member
View Badges
Joined
Mar 2, 2016
Messages
2,592
Reaction score
1,814
Location
Potomac
Rating - 0%
0   0   0
A skimmer (or any type of aeration) will not boost pH if the room has elevated CO2 in the air. That is by far the most common cause of low pH in a reef tank.

A skimmer using elevated CO2 house air is very effective at countering other methods to raise pH as it will quickly drive down pH with CO2.

The opposite is true when using a skimmer with a CO2 scrubber or outside air.
 

Randy Holmes-Farley

Reef Chemist
View Badges
Joined
Sep 5, 2014
Messages
66,550
Reaction score
62,845
Location
Arlington, Massachusetts, United States
Rating - 0%
0   0   0
A skimmer using elevated CO2 house air is very effective at countering other methods to raise pH as it will quickly drive down pH with CO2.

The opposite is true when using a skimmer with a CO2 scrubber or outside air.

Yes, I agree.
 
OP
OP
arking_mark

arking_mark

2500 Club Member
View Badges
Joined
Mar 2, 2016
Messages
2,592
Reaction score
1,814
Location
Potomac
Rating - 0%
0   0   0
Just a quick update.

For the last couple of weeks, we have had the full family home and my setup is no longer able to keep such a tight pH, especially at night when all 6 of us and the dog are at home.

I've also increased the the in-tank water flow with a wave maker and reduced the pH setpoint down to 8.28.

With this setpoint, I should see swings between 8.25 and 8.31. However, I'm seeing lows of about 8.22 at night.

Recently, one of the kids was away for a night and that night the system had no problems keeps the expected +/- 0.05 hysteresis.

One further note is that recently, my magnetic kalk stirrer has been spiking the tank when mixed. I'm sometimes seeing a rapid 0.04 jump right when the stirrer kicks in. I attribute this to the fact that the stirrer creates a vortex that increases the level in the container and doses additional and maybe even some Kalkwasser slurry.

Now that I have coralline algae growing everywhere, I plan on further lowering the pH to reduce abiotic precipitation. I'll probably come down to 8.26 as the setpoint.
 

jphilip813

Well-Known Member
View Badges
Joined
Sep 8, 2019
Messages
884
Reaction score
570
Location
In The 915
Rating - 0%
0   0   0
Just a quick update.

For the last couple of weeks, we have had the full family home and my setup is no longer able to keep such a tight pH, especially at night when all 6 of us and the dog are at home.

I've also increased the the in-tank water flow with a wave maker and reduced the pH setpoint down to 8.28.

With this setpoint, I should see swings between 8.25 and 8.31. However, I'm seeing lows of about 8.22 at night.

Recently, one of the kids was away for a night and that night the system had no problems keeps the expected +/- 0.05 hysteresis.

One further note is that recently, my magnetic kalk stirrer has been spiking the tank when mixed. I'm sometimes seeing a rapid 0.04 jump right when the stirrer kicks in. I attribute this to the fact that the stirrer creates a vortex that increases the level in the container and doses additional and maybe even some Kalkwasser slurry.

Now that I have coralline algae growing everywhere, I plan on further lowering the pH to reduce abiotic precipitation. I'll probably come down to 8.26 as the setpoint.
Do you have a photo of your Co2 Scrubber set-up along with the skimmer and solenoid? I am looking to set one up myself and trying to see what a good set-up looks like....hard to find on YouTube. I have the Ice Cap Co2 scrubber
 

Mastering the art of locking and unlocking water pathways: What type of valves do you have on your aquarium plumbing?

  • Ball valves.

    Votes: 43 48.3%
  • Gate valves.

    Votes: 47 52.8%
  • Check valves.

    Votes: 20 22.5%
  • None.

    Votes: 23 25.8%
  • Other.

    Votes: 9 10.1%
Back
Top