Risks with high alkalinity?

[jenpen400]

When I filled our AGP a year ago CH was 210 and ALK was 320. I was able to drop the ALK down to 110 but it is much harder to push down from a high number. Once I got the Alk to 220 it was easier. I know how you feel add acid, arate Alk goes down now add water to make up for evaporation and back up it goes. I found that just putting the fountain on low and keeping the ph around 7.4 or lower the alk just keeps creeping down without as much evaporation. Now my alkalinty is fine and my CH is 340. Oh well I guess thats another thread.

Hope this helps
jennifer

[chem geek]

When I filled our AGP a year ago CH was 210 and ALK was 320. I was able to drop the ALK down to 110 but it is much harder to push down from a high number. Once I got the Alk to 220 it was easier. I know how you feel add acid, arate Alk goes down now add water to make up for evaporation and back up it goes. I found that just putting the fountain on low and keeping the ph around 7.4 or lower the alk just keeps creeping down without as much evaporation. Now my alkalinty is fine and my CH is 340. Oh well I guess thats another thread.

Hope this helps
jennifer

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

[Tredge]

Hi Rangeball!

My pool is Still at 340 Alk and I havent bothered to lower it.
Water is 'crystal' clear and no scaling problems.

My CA hardness is quite low...almost 0.
PH stabalizes at ~7.8 but I try to knock it down to 7.4 every few days.

My TDS is quite high due to the SWG. At around 3000 TDS currently.

Hope that helps, I've been happy with the pool and the alk hasnt bothered me a bit.

[chem geek]

My pool is Still at 340 Alk and I havent bothered to lower it.
Water is 'crystal' clear and no scaling problems.
My CA hardness is quite low...almost 0.
PH stabalizes at ~7.8 but I try to knock it down to 7.4 every few days.
My TDS is quite high due to the SWG. At around 3000 TDS currently.

For what it's worth, the pH stabilization at 7.8 is "predicted" by my spreadsheet and the CO2 graph except that on the graph I made it's off the chart (looks like I need to make a new graph for you high alkalinity folks ). As for your calcium hardness, you really don't want it to get to 0 if you have a plaster/grout pool. The problem with near 0 calcium isn't scaling, but corrosion (not of metal, but of plaster/grout). Is your pool vinyl? Is your CYA near 80 since you have an SWG? Mostly I'm asking just to get a sense of everyone's pool so I can see where the models start to break down.

Richard

[Rangeball]

Hey Tredge Glad things are working in your favor

Mostly I'm asking just to get a sense of everyone's pool so I can see where the models start to break down.

Richard, my pool fyi-

21,200 gal IG vinyl, 3' to 8' depth.
Last time I tested fill water- PH 7.2, ALK 320.
Chlorinated with .75 gal of 6% bleach nightly. Salt approx 1200 ppm, no SWG.

I ran some tests when I was home for lunch.

TC/FC- 3.0
PH- 7.6
ALK- 170
CYA- 20ish

I was gone the past 3 days, and right before I left the PH was 8+. I added some muratic acid, and this is where things stabilized when I returned.

I highly suspect that with anymore splashing about (another kid fest), my PH will again shoot rapidly up. I always panic when it does because my test kit's upper range is 8.2, and I don't want it to get above that level but won't be able to tell if it does, so I knock it back down. What conditions would it take for my pool to go much higher than 8-8.2?

[chem geek]

TC/FC- 3.0
PH- 7.6
ALK- 170
CYA- 20ish
What conditions would it take for my pool to go much higher than 8-8.2?

Well interestingly the pH of 7.6 with alkalinity of 170 gives the same "somewhat stable" relative outgassing rate as with Tredge -- his was just over 15 and yours is almost 14.

As for what conditions it would take for your pool to keep rising in pH -- it will always rise until it reaches equilibrium, but the rate of rise will keep slowing down. Unfortunately, it is largely a function of the amount of aeration of your pool so yes, having your kids over and splashing will force up the pH faster. This is not something easily predictable -- it's more something you'll have to keep track of and have a "feel" for. I can tell you that with the "calm" conditions you are now seeing, that a pH of 8.0 will outgass CO2 at about one-third the rate as it is doing now at 7.6 pH so the pH will rise about one-third as fast (again, assuming similar aeration conditions). Aeration is also caused by wind. Basically, only a pool cover would give you a stable and relatively predictable system. Even so, it's kind of eerie that I've now seen several cases that all stabilize near this relative "15" number.

On the other hand, there are those in the rising ph levels thread who experience relatively large pH upward movement without abnormal aeration and with outgas numbers below 15 -- but some of them also do not see the slow drop in alkalinity over time so something else other than CO2 outgassing is causing their pH to rise -- we just haven't figured out what it is.

[EDIT]The number "15" means that the amount of dissolved carbon dioxide in the pool is 16 times larger than the equilibrium amount which is where it would eventually end up if it continued to outgas to air -- that's how far out of equilibrium the pool system is (or how "carbonated" it is).[END-EDIT]

Richard

[Rangeball]

Thanks Richard.

What would I have to get my ALK to to get PH to stabilize no higher than 7.6?

If this were your pool, what would be your plan of attack? Lower ALK to x each time you have to add fill water?

[Tredge]

For what it's worth, the pH stabilization at 7.8 is "predicted" by my spreadsheet and the CO2 graph except that on the graph I made it's off the chart (looks like I need to make a new graph for you high alkalinity folks ). As for your calcium hardness, you really don't want it to get to 0 if you have a plaster/grout pool. The problem with near 0 calcium isn't scaling, but corrosion (not of metal, but of plaster/grout). Is your pool vinyl? Is your CYA near 80 since you have an SWG? Mostly I'm asking just to get a sense of everyone's pool so I can see where the models start to break down.

Richard

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

[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?