Risks with high alkalinity?

[jenpen400]

Jennifer,

I just want to understand clearly. Are you now at an alkalinity of 110 or 220? Is the evaporation less because you've got the fountain on a lower setting? So now you have a balance between losing alkalinty through the aeration (and adding acid to restore the pH) and gaining alkalinity from make-up water for evaporation. Is that right? So your alkalinity is stable, but aren't you adding a lot of acid frequently to keep your pH down? I suppose that may be the tradeoff necessary.

Evap. --> Make-Up --> Alk. Up
  ^                       V
  |                   Fountain
Alk. Down                 V
pH Down <---- Acid <---  pH Up

Is that your cycle?

Richard

Last test alkalinity was 140 down from 160 due to lots of evaporation and high fill water. Yes this takes a lot of acid. What I have found is that vigorously aerating it seems I evaporate more water with out rising the ph faster. It could be that more water makes it over the side but the top rail seems dry??? When I get the alkalinity where I want it I just ripple the surface with the jet and even though I replace an inch or two a week it alkalinity and ph remain 110 and 7.5-7.8 with out adding much. I have never needed to raise my ph and my fill water has a ph of 7.5 Hope I did the quote thing right it's my first time.

jennifer

[chem geek]

Jennifer,

You did great. Thanks for the info. You may have hit on a procedure that may work well for people with high alkalinity tap water. We'll see how Rangeball does with it!

Richard

[chem geek]

I have a heavy epoxy coating on the pool so the grout and plaster are protected.

I have my CYA at 40. I'm reluctant to follow instructions and bump it to 80

OK, thanks for the info. As for the CYA level in SWG pool systems, this is a matter of vigorous discussion at CYA for Salt Chlorinator Pools II in The China Shop. It appears that for most people, following the manufacturers recommended 70-80 ppm CYA level makes the salt cell run more efficiently (your manufacturer may have a different optimum level, but most are pretty high) probably due to the CYA taking away and tying up chlorine away from the generation plates of the cell. Otherwise, too much chlorine builds up near the plates and slows down the generation process. This means that at lower CYA levels you have to have your cell running at higher power and/or longer times in order to achieve the same FC level.

There isn't that much debate about this efficiency improvement with higher CYA. The main debate is over whether Ben's CYA table still needs to be applied -- do you have to have higher FC to prevent algae (disinfection levels still seem OK). Many people do OK, but some do not, so the jury is still out and it's a hotly debated topic. I'm just letting you know what's up -- you should obviously do whatever you feel comfortable with. It's too bad that it's not easy to lower CYA once you've raised it; otherwise, you could just experiment with this.

Richard

[Tredge]

OK, thanks for the info. As for the CYA level in SWG pool systems, this is a matter of vigorous discussion at CYA for Salt Chlorinator Pools II in The China Shop. Richard

I've followed that discussion since the beginning. I see no evidence why Ben's chart wouldnt apply so I'm sticking with that. Efficiency isnt my main goal, a clean and safe pool is

To stay on topic, if I follow your recommendations about a high ALK...its ok to run a pool at 7.8PH? Does this apply to a SWG pool since the generator is far more efficient between 7.2 and 7.6?

[Rangeball]

Jennifer,

You did great. Thanks for the info. You may have hit on a procedure that may work well for people with high alkalinity tap water. We'll see how Rangeball does with it!

Richard

Just found out last night that we're having another kid fest Thursday night. Aeration x 100

I plan to lower my PH to around 7 pre party and let them have at it. I'll test the next morning to see where things leveled out.

[Tredge]

Just found out last night that we're having another kid fest Thursday night. Aeration x 100

I plan to lower my PH to around 7 pre party and let them have at it. I'll test the next morning to see where things leveled out.

Aeration X100 means a much faster rise in PH. I'd consider adding Acid mid-party to maintain the PH at ~7. Put those kids to work!

[Rangeball]

Aeration X100 means a much faster rise in PH. I'd consider adding Acid mid-party to maintain the PH at ~7. Put those kids to work!

From Jen's post above-

What I have found is that vigorously aerating it seems I evaporate more water with out rising the ph faster.

I'm confused. Which one is right?

[chem geek]

To stay on topic, if I follow your recommendations about a high ALK...its ok to run a pool at 7.8PH? Does this apply to a SWG pool since the generator is far more efficient between 7.2 and 7.6?

Well, the SWG guys say, and many users of SWG pools who report in this forum say, that CYA of 60-80 (70-80) is also much more efficient so I'm not sure how to respond. I suppose that operating at high alk and higher pH may not be a good idea with an SWG system because it is less efficient (based on what you just said).

I agree that you are being safe and prudent to follow Ben's table with an SWG system. I was just pointing out that this is an area of active debate and I do not consider final conclusions to be drawn yet.

Richard

[chem geek]

I'm confused. Which one is right?

From a technical point of view, more aeration means more outgassing of CO2 which means more of a rise in pH. However, there may be a point of diminishing returns and that may be what Jen saw -- that vigourous aeration caused more evaporation but not a noticeable increase in pH. She wasn't saying that aeration did not cause a rise in pH, but rather that extra vigorous aeration didn't seem to make the pH rise much faster but did increase the evaporation rate quite a bit. She found that a good tradeoff was made by doing some aeration that was less vigorous.

The processes that determine the rate of outgassing and evaporation are very complicated. Both depend on the surface area of the air-to-water boundary (including that boundary in droplets) but the specifics of the rates may be quite different. Nevertheless, if certain droplets were to completely evaporate, then you would lose both the water and the carbonate in that water into the air leaving only some salt (like sea spray) to eventually fall back to the ground or get whisked away by wind.

So I don't have an explanation for Jen's observation of an increase in evaporation without an increase in pH. I could imagine that there is a small increase in pH but that the rate of evaporation increases much more so that it appears that it dominates what's going on. The evaporation process may have a non-linear and more rapid runaway effect compared to the CO2 outgassing, but that's just a wild guess on my part.

Richard

[Rangeball]

Ok.

I plan to add the acid and drop the PH as low as possible tomorrow morning so the pool will be ready for them swimming 10 hours later. However, they are now calling for scattered thunderstorms, but I guess I'll still be ok if it rains and we call the kids off because I've noticed rain is one heck of an aerator also