Risks with high alkalinity?

[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?

[court475]

I'm very interested in this thread. We got a new A.G. pool last week and my fill water Alk was very high, 370 I believe, and Ph was 8.2. I've gotten the Ph down a bit, and the Alk a little as well, but not much. We are adding a fountain today and I hope that helps. With being a newbie it all has my head "swimming"!

Courtney

[Rangeball]

court, read the "lowering alk" sticky over and over. It does indeed work just like it's typed.

One thing I would highly recommend based on my experience is to not use the fountain to aerate UNTIL you get the ph down to where you want it. Monitor the PH and when it rises to the point you need to knock it back down again (assuming you still need to lower your alk some more) turn off the fountain and again lower your PH, then begin aeration.

Good luck

[chem geek]

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?

The short answer is I don't really know.

Jennifer pushed her alkalinity way down to a normal range where there would be little pH rise from outgassing and she had a slow but definite amount of aeration to intentionally make the pH rise so that when she added acid she lowered alkalinity. This was to compensate for the the alkalinity she was adding through make-up water for evaporation.

You are already down to 170 TA and have fill water that is 320 TA so I would say "go for it" -- do what Jennifer did and use Ben's method to push your TA down further. What you and Jen had are close to the level of "15", but I'll list for you below the pairings of pH and TA at this level and at "10" which has 2/3rds of your current outgas rate.

       Level 15  Level 10
pH 8.0  460 TA   320 TA
pH 7.9  365 TA   255 TA
pH 7.8  290 TA   205 TA
pH 7.7  230 TA   162 TA
pH 7.6  185 TA   130 TA
pH 7.5  150 TA   105 TA
pH 7.4  120 TA    85 TA
pH 7.3   95 TA    68 TA
pH 7.2   77 TA    55 TA
pH 7.1   63 TA    45 TA
pH 7.0   51 TA    37 TA

Jennifer is close to the 7.4/120 level and you are close to the 7.6/185 level. So you can continue to push down to her level or because of your kids and their extra aeration you can choose to go down even further to a TA of 85 and a pH of 7.4 (or perhaps a TA of 105 and a pH of 7.5) which should have much less acid demand than you are now experiencing. Just remember Jennifer's "trick" of intentionally allowing for some amount of aeration which will cause pH to rise and then you add acid to bring the pH back down and reduce alkalinity. You should try and do this to the extent you need to for the make-up water that you add to fill-up from evaporation.

The other major alternative you have is to not fight the pH so much and live with a high alkalinity and high pH system. You've been there and don't like it, so that's probably not a good choice.

You asked what I would do. I would get a pool cover and avoid this whole mess. However, if that's not practical, economical, or is too much work, then I think Jennifer's approach is a good one to try.

Richard

[Rangeball]

Thanks.

I'll read that several more times in hopes I can understand it

I had similar experience to Jenn. When my alk was way up, it was hard to move.

Now that I have it below 200 it drops much more readily. I should probably lower it again since I have a few inches before I'll have to add more water to get it down to make subsequent drops easier.

[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