My experience with CO2

[cliff_s]

I built a CO2 system and used it for a couple of years. I used my home automation
to time the injection. In fact I still have a 20lb CO2 bottle that is empty.

In my experience it didn't work out too well. I live in AZ and it gets hot here.

The CO2 bottles are under very high pressure and if the bottle gets too hot
the excessive pressure valve trips and dumps the whole cylinder(this happened several
times). The gaskets that are between the regulator and the cylinder are plastic
and when they get hot they soften and then the CO2 leaks(lost a couple of bottles
of CO2 this way). Ended up being a expensive pain so I disconnected it.

My experience with CO2 was this, it did bring down the pH rather quickly,
but it was gone just as quickly. It was hard to keep a consistent pH during the
day. I think it would work fine in a commercial pool where the pump ran 24 hours
and the CO2 could be injected continuously. A home pool this really doesn't work
because the filter pump is only run about 6 hours at night(cheaper electric rates).

I plumbed the system with copper tubing and it seemed to hold up fine. I injected the
CO2 into my floor cleaning system so the CO2 was injected into the bottom of the pool.
The 20lb bottle would only last about 3 weeks in the summer(if it didn't leak or vent). This
made the operating cost twice as much as just using acid.

In a previous house I used a peristaltic pump to add acid to the pool and this system
seemed to be easier to use and trouble free. I used a 15 gal barrel and diluted the acid
3 to 1, which made it 10%. One of my future projects is to install a peristaltic pump
to add acid to this pool. With a 15 gal full barrel and a 3 to 1 dilution the barrel will last about
6 to 8 weeks.

Anyway this was my experience with CO2.

Cliffs

 

[chem geek]

Thanks for the info. If one is using CO₂ for pH control, then right off the bat it means that the TA level is too high and should be lowered first. Adding carbon dioxide to the water to lower the pH because of carbon dioxide that raises the pH is just a yo-yo that should be stopped by lowering the TA. Ideally, the TA will be low enough for very little carbon dioxide outgassing and the only source of pH rise will be excess lye in bleach or chlorinating liquid that is compensated by a small amount of acid addition. Of course, that's ideal and in practice we don't bring the TA so low as to completely eliminate outgassing.

 

[learthur]

Interesting stuff.

Thanks for your post!

 

[cliff_s]

An addition to my previous post:

My current pool has a SWG and that is the reason for trying CO2. Normal operation of the SWG
tends to raise pH. During the summer when the pool water temp. is above 80deg F the SWG has to work harder
to keep up with the chlorine demand hence the greater effect on the pH.

Adding acid to control the pH does work but has a side effect in that it also lowers TA. I found a compromise
is for the pH to be 7.6 to 7.7 to hold the TA about 50 to 60. Using CO2 has little effect on the TA in the
pool and will lower the pH without excessive lowering of the TA. Although acid has to still be added to
control the TA even when using CO2. If the pH is allowed to get any higher then there is a calcium precipitation
problem. This is common when the fill water is from wells that draw the water from limestone aquifers.
The calcium content keeps rising because it doesn't evaporate with the water and more calcium is added
with the fill water.

Sure, frequent changing of the pool water will keep the calcium content lower, but there is a cost trade off.
25,000 gals. of water isn't cheap and 600 lbs of salt isn't either, so water changing is only done when
absolutely necessary.

In my experience pool chemistry changes very slowly do to the large quantity water involved. Several years ago I did
look into some of the automated systems. pH probes are rather high maintenance and quite expensive. My conclusion
was that the parameters change so slowly in a home pool that automatic control is not necessary. If you have a
commercial pool with all of a sudden 25 10 year olds jump in, then that is another story.

With a little tweaking a peristaltic system for either both chlorine and acid or just acid will work fine. The peristaltic
pumps are about $200 and a 15 gal barrel(used) $20. With plastic plumbing you are looking a less than $250 for
a system. The pumps have a knob for speed adjustment to control the acid injection. A timer can be also added
depending on your need. You will only need the smallest pump you can buy as the amount of chemical addition is
very small at any one time. Using a SWG with a peristaltic pump and a 15 gal barrel for acid you will only have to fill the
barrel every 6 to 8 weeks. This way you can go on vacation and not have to worry about your pool.

Not having to due anything(except check chemistry parameters) less than once a month is right up
my alley.

Happy Swimming,

Cliffs

 

[JasonLion]

If you add borates you can then lower TA even further and the PH increase should stop.