Poolsmith CO2 injection for pH control

cptkirk

Well-known member
Jul 29, 2018
208
FL Panhandle
I'm not seeing that level of stability, however my operating conditions are probably a bit different here in the FL panhandle. My system was off for around 4 days while I waited for the new pressure sensor connector to come in, and I had to add some acid to knock the pH down a bit after it climbed above 8.0. But the pool is getting used every day, and the heater is typically running for a couple of hours. Water temperature is high 70's to low 80's. I have my system set up to inject at 1.5 CFPH every day at a 180 setting (which is between 4 and 5 hours) and that seems to work well for my pool. The pH has been very stable at 7.7 every morning before injection starts up again.

I think I'm getting close to emptying my first 20 lb. tank after about 5 weeks (the pressure gauge had been reading about 500 psi consistently, but now has dropped to around 200). However, I had been running at a higher consumption rate for most of that time than I currently am, so the next tank should be a better predictor of my longer term consumption rate.
 
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bonsey

Well-known member
Oct 7, 2018
131
PA
I use the Hayward Sense and Dispense system with Co2 injection. No issues so far as far as pH and the injection system, very stable and keeps my ph at 7.6 (recommended level by Hayward). Here in NEPA there are plenty of places that you can either exchange a Co2 cylinder or get it refilled. It costs me about $15 to refill a 15lb cylinder. I just started last year with a 20lb cylinder but I am not quite sure how long it lasted because I did not check it until I opened this year and it was empty. So not sure exactly when it went empty last year.

Ps... the best way to check how much you use is to weigh the cylinder (if you can). Since it is a liquid, the pressure gauge will always read about ~500 until one day it will crash and be emtpy.
 

Bperry

Gold Supporter
Aug 20, 2020
988
Knoxville, TN
Pool Size
27000
Surface
Plaster
Chlorine
Salt Water Generator
SWG Type
CircuPool RJ-60
I read the site requires you to use aluminum tanks? If you do the exhange, make sure you get aluminum back as the CO2 exchanges around here tend to have steel tanks. I was able to get a refill from a paintball equipment supplier.
 

cptkirk

Well-known member
Jul 29, 2018
208
FL Panhandle
I think I'm getting close to emptying my first 20 lb. tank after about 5 weeks (the pressure gauge had been reading about 500 psi consistently, but now has dropped to around 200).

Even though the pressure gauge on the tanks dropped to what reads as zero a few days ago, I'm still getting gas flow at the meter on the controller and pH has remained in the same range. Will continue to watch it to determine when it actually runs out on this first tank.
 

Prickly

Well-known member
Jul 8, 2020
127
Kelowna
Pool Size
31000
Surface
Fiberglass
Chlorine
Salt Water Generator
SWG Type
Hayward Aqua Rite (T-9)
Even though the pressure gauge on the tanks dropped to what reads as zero a few days ago, I'm still getting gas flow at the meter on the controller and pH has remained in the same range. Will continue to watch it to determine when it actually runs out on this first tank.
Have you had cold weather lately? I believe that can cause the pressure to drop quite a bit
 

cptkirk

Well-known member
Jul 29, 2018
208
FL Panhandle
Don't think it's a temperature thing. It had been consistently right around 500, then started to drop over the course of a few days and hit zero about three days ago. I guess the scale is large enough that low pressures don't register.
 

JoyfulNoise

TFP Expert
Platinum Supporter
May 23, 2015
18,585
Tucson, AZ
Pool Size
16000
Surface
Plaster
Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-60
Have you noticed any changes in CO2 flow with changes to your pump speed?
 

cptkirk

Well-known member
Jul 29, 2018
208
FL Panhandle
I mostly run my pump at around 1700 rpm 24x7. I occasionally speed it up when I'm vacuuming or if there is pollen or other stuff floating on the surface I want to skim more quickly. There is a minimum speed that the pump has to run to trigger the pressure sensor in the CO2 controller. I haven't experimented enough to discover the lower limit exactly, but it's not too much lower than my normal speed. Probably pretty close to what it takes to run the heater.
 
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cptkirk

Well-known member
Jul 29, 2018
208
FL Panhandle
First tank ran completely empty. It's been 6 weeks since I first turned on the system, but I was running at a higher flow rate for the first couple of weeks. So I'm expecting I'll get 7 to 8 weeks per tank.
 
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Prickly

Well-known member
Jul 8, 2020
127
Kelowna
Pool Size
31000
Surface
Fiberglass
Chlorine
Salt Water Generator
SWG Type
Hayward Aqua Rite (T-9)
Any updates?
I haven't had any issues with it yet. I'm running it on saver mode at 1 CFPH and it's keeping my pH steady between 7.5 and 7.6. I'm happy. I suspect my use will go up once it's summer and the cover is off more and the kids are splashing around.
 

cptkirk

Well-known member
Jul 29, 2018
208
FL Panhandle
Since I have fairly steady pH rise, I've been injecting every morning starting around 7:00 am over a 4+ hour interval at a rate of 1.5 CFPH. It only injects during half of that interval, so daily usage is around 3 CF. Typically my pH is about 7.7 in the morning before it starts injection and about 7.5 when injection completes. TA has been fairly steady, although it has creeped up a little (between 80 and 90).

For me it has made a big difference in convenience. The only acid I've added in nearly 7 weeks has been when I had turn the system off for 4 days awaiting a replacement part. Previously I was having to add a quart every 3 to 4 days. I found a place that will do a 20 lb. tank exchange for $25, so the acid cost and CO2 cost are pretty close if I go that route, and I'm not having to add baking soda to compensate for all the acid I was dumping in. Since salt, CH, and CYA are fairly constant unless I get dilution from rainstorm overflow (I rarely need to backwash my filter after pollen season ends), and my SWG has no problem keeping FC at my desired targets, I'm not regularly adding anything to the pool.
 

JamesW

TFP Expert
Mar 2, 2011
28,200
TA has been fairly steady, although it has creeped up a little (between 80 and 90)

If you lower that to 60 to 70 ppm, the amount of CO2 needed should be reduced.

Also, if you keep the pH higher, the amount of CO2 needed will be reduced.

Here are the percentages of carbonic acid (carbon dioxide) vs. bicarbonate based on pH.

pH.......H2CO3........... HCO3-
7.2........12%................88%
7.3........10%................90%
7.4..........8%................92%
7.5..........7%................93%
7.6.........5%.................95%
7.7.........4%................96%
7.8.........3%................97%
8.0........2%.................98%

As you can see from this, the amount of carbon dioxide (carbonic acid) is 2.33 times lower at a pH of 7.8 vs. a pH of 7.5, which implies that the amount of carbon dioxide needed to maintain a pH of 7.8 will be about 2.33 times less than keeping the pH at 7.5.
 
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cptkirk

Well-known member
Jul 29, 2018
208
FL Panhandle
My TA has been creeping up slowly, to where it reached 100. We haven't had any rain for a while, but my fill water TA is only 70, so not really sure why the increase. I decided to try to knock the TA back down to around 70, so I turned the CO2 injection off and have been adding a quart of acid each day for the past three days. It has been a slower process than I thought, only down to 90 after today's dosing. I'll likely finish off this gallon of acid tomorrow, guess I'll have to buy some more to complete the task.
 

Prickly

Well-known member
Jul 8, 2020
127
Kelowna
Pool Size
31000
Surface
Fiberglass
Chlorine
Salt Water Generator
SWG Type
Hayward Aqua Rite (T-9)
My TA has been creeping up slowly, to where it reached 100. We haven't had any rain for a while, but my fill water TA is only 70, so not really sure why the increase. I decided to try to knock the TA back down to around 70, so I turned the CO2 injection off and have been adding a quart of acid each day for the past three days. It has been a slower process than I thought, only down to 90 after today's dosing. I'll likely finish off this gallon of acid tomorrow, guess I'll have to buy some more to complete the task.
My TA has crept up as well. It has increased by at least 10 ppm since I started using CO2
 

mknauss

Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
44,310
Laughlin, NV
Pool Size
6000
Surface
Fiberglass
Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-40
fill water TA is only 70, so not really sure why the increase.
Evaporation. When water evaporates, it leave the TA compounds behind. You add 70 TA fill water and the overall TA of the pool water rises.

CO2 does not remove TA. Only acid does.
 

cptkirk

Well-known member
Jul 29, 2018
208
FL Panhandle
Finally got my TA down to 70 after adding two gallons of MA over the course of 9 days. Last dose was applied yesterday morning. This is the first time I ever deliberately tried to lower the TA so didn't know quite what to expect. It's been exceptionally dry for the past several weeks with no rain to speak of, so I think that accounts for the rise I experienced. My pH is currently 7.4. I will turn the CO2 system back on today to see how this impacts my usage going forward.
 

cptkirk

Well-known member
Jul 29, 2018
208
FL Panhandle
Before lowering my TA, I was typically seeing a daily pH increase of around .2 (for example, from 7.6 to 7.8) if nothing was added. It now looks like it is increasing by about .1. My previous settings that were adding about 3 CF of CO2 each day appear to be more than I need, so starting tomorrow will decrease to 2 CF per day to test the effect.
 
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cptkirk

Well-known member
Jul 29, 2018
208
FL Panhandle
Update: my TA rose back up to 80 pretty soon after I had lowered it to 70 using MA. It has stabilized there, and I'm just letting it be. We have been getting much more regular rainfall since the drier conditions ended a few weeks ago so there probably hasn't been much water added via the autofill. I'm operating where I was before at 1.5 CFPH for just over 4 hours (so just over 2 hours of actual CO2 injection), with pH typically right around 7.8 when measured first thing in the morning before injection starts for the day. The pressure on the second tank has begun to drop, but has not reached zero yet. Based on past experience with the first tank, I probably have around another 5 days or so before it is completely empty. I've been operating on this tank since mid May, but it was switched off for about 9 days when I was lowering TA using MA. So it will probably end up at around 7 weeks of actual usage.
 

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