I've read and trust that this works, but can someone explain why or how aerating raises the PH?
Aeration to raise PH
- Thread starter rwrogers11
- Start date
Pools are intentionally over-carbonated in order to help saturate the water with calcium carbonate to protect plaster surfaces and to provide a pH buffer to prevent large swings in pH from chemical addition, bather load, etc. However, this means that there is more carbon dioxide in the pool than there would be if in equilibrium with the carbon dioxide in air. So carbon dioxide outgasses from the water into the air. Aeration increases the surface area of the water-air interface and that increases the rate of such carbon dioxide outgassing.
When carbon dioxide leaves the water, this is essentially removing carbonic acid from the water (carbon dioxide combined with water is carbonic acid). When you remove an acid from water, the pH rises. For technical reasons I won't get into too much here, the TA doesn't rise because carbonic acid is a weak acid so removes two components that have opposite effect on TA so they cancel out (removal of hydrogen ions raises TA while removal of carbonate/bicarbonate ions lowers TA).
The bottom line is that to ultimately lower the TA you have to remove some of the carbonates from the water. It's the opposite of adding bicarbonate to increase the TA. However, there is no direct way to remove bicarbonate itself so we aerate to more quickly remove carbon dioxide which is in equilibrium with bicarbonate and then add a strong acid to lower the pH and TA.
Hope that helps.
When carbon dioxide leaves the water, this is essentially removing carbonic acid from the water (carbon dioxide combined with water is carbonic acid). When you remove an acid from water, the pH rises. For technical reasons I won't get into too much here, the TA doesn't rise because carbonic acid is a weak acid so removes two components that have opposite effect on TA so they cancel out (removal of hydrogen ions raises TA while removal of carbonate/bicarbonate ions lowers TA).
The bottom line is that to ultimately lower the TA you have to remove some of the carbonates from the water. It's the opposite of adding bicarbonate to increase the TA. However, there is no direct way to remove bicarbonate itself so we aerate to more quickly remove carbon dioxide which is in equilibrium with bicarbonate and then add a strong acid to lower the pH and TA.
Hope that helps.
My system is setup as spa spillover whenever pool pump is running. I guess I am aerating all that time? Maybe this is why (along with SWCG) my pH is always high :-(
Do waterfalls and spa spillovers adversely affect the pH levels?
Do waterfalls and spa spillovers adversely affect the pH levels?
If one cannot turn off waterfalls or otherwise reduce the aeration, then the only way to avoid the pH rise is to significantly lower the TA level. Some have lowered it down to 50 ppm or even a bit lower. If one does that, then one needs to raise the CH level and pH target to keep the water in balance for plaster pools. Normally, we recommend 70 ppm for SWCG pools, but that may not be low enough for some pools. We know that for spas using the Dichlor-then-bleach method, that 50 ppm TA works much better due to the heavy aeration from spa jets and the higher water temps.
chem geek said:
Yeah, totally true from my very layman point of view. Had TA at 80-100 in my spa and had to keep adding acid. Now that I brought TA down to 50, I only add acid every 1 1/2 weeks or so.
Thanks, Chem Geek and beezar,
Maybe I'm part of the way there as my CH is a ghastly 600+ ! My TA is ~ 120 so I will look into the factors needed to lower it. thepoolcalculator says add a bunch of MA and aerate. I will also look into reconfiguring the PS-8 to return the spillover to manual mode - I seem to recall the solar guy showing me how my valves were cammed to equalize pressure on the return path, in consideration of the spa spillover. I'm not at the house right now so I will take a look later. Thanks again.
Maybe I'm part of the way there as my CH is a ghastly 600+ ! My TA is ~ 120 so I will look into the factors needed to lower it. thepoolcalculator says add a bunch of MA and aerate. I will also look into reconfiguring the PS-8 to return the spillover to manual mode - I seem to recall the solar guy showing me how my valves were cammed to equalize pressure on the return path, in consideration of the spa spillover. I'm not at the house right now so I will take a look later. Thanks again.
Every time I spend some time on this site I learn something. Thanks chem geek for the explanation on aeration and PH. I had to increase my CYA and CH the other day. After everything was circulated my PH dropped down to 7.4 . Aerated with the waterfall for 2 days (12 hrs per day) and my PH is now 7.6 . Pretty cool.
Thanks guys
Thanks guys
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