pH drifting up

[presence52]

Hi! Back when our pool's CYA levels were in the 90s-100s, we'd target FC of 11-12 and only need to add about 2 pints of 8% bleach daily.

After replacing water, CYA is now lower at 55, but we've noticed a few things:
1) Chlorine consumption is going up, needing 3-4 pints daily, even though FC target is lower at 7-8. I read an old post that CYA may have a "shielding effect" at higher levels disproportionate to the chlorine levels, so this might explain it.
2) pH is creeping up. Is this because there's less CYA which is a weak acid and has buffering power? Pool is now needing 1-2 pints of 31.45% hydrochloric acid once to twice a week. Yikes. TA started out at 120, and I've been hoping that once multiple additions of acid brought the TA down, we'd reach an equilibrium point... but this still has not happened and TA is now lower limit of recommended range at 80.
3) The chlorine consumption seems to be mitigated a bit when the pH is in the ideal range. I wonder if this has something to do with hypochlorous acid having a longer half-life and being more effective at killing stuff than hypochlorite ion. Even when pH is ideal, the pool is still eating up more chlorine than when the CYA was crazy high.

CURRENT POOL STATS
FC 3.5 (CC 0) - yes, I know need to add some now
CYA 55
pH 7.8 (needs 1 and 2 drops of acid demand reagent to go down to 7.4 and 7.2, respectively)
TA 80
CH 100

TAP WATER STATS
pH 8
TA 70
CH 80

What should we do? I know it's wrong, but I'm kind of tempted to drive the CYA back to where it was before, since things seemed to be easier back then!

And yeah, I know the calcium level is not ideal but I want to wait until the pH is stable at a lower level to prevent precipitation fun. However, I'm told there is a 24 hour waiting period between chlorine and calcium additions, and I'm not sure how I'm going to achieve this when I'm adding chlorine every 24 hours.

 

[Jezza]

You could have been caught out with algae which is now consuming chlorine disproportionally to what you were experiencing before. I'd run an OCLT before you add any more CYA at this stage to rule out that possibility. How does the water look?

You may find that your pH will stabilise at a lower level than 80. Many members find that their pH stabilises around 50-60 TA so I would just continue to add acid as required and hopefully you'll find your happy point. Also lots of splashing and aeration can push pH up.

 

[presence52]

Thanks Jezza. We have done the OCLT several times without any loss. We've even done multiple checks throughout the day, and the majority of the loss is happening in the early afternoon hours.

 

[planoattorney]

Jeez:

Quick follow up question; I was under the impression that a low TA is not good. What is the effect of low TA in a plaster chlorine pool?

I ask because I have had the same problem as OP. My Ph seems to creep up and I am adding acid on a regular basis this year. OCLT are good, CC is zero every time I test (so much so that I am starting to wander if my #3 reagent is bad). Last night I dumped in a lot of acid, circulated the pool and added 4# of Borax to push my borates back over 50. This morning my Ph is 7.2 but my TA is 50. Should I just let things be and see if the acid demand continues or should I aerate and get my TA up?

FC = 4
CC= 0
Ph = 7.2
TA = 50
CA = 350
CYA = 40

 

[7snorkel]

Plano,
I'm in your city, & i burn 3ppm of chlorine daily in Summertime. 9-10 hours of sun.

my cya is 50.
my FC stays between 5-8ppm.
I'm religous about keeping FC 2ppm above minimum(3ppm)
i hope you're not keeping PH at 7.2.

Let it drift up to 7.8, then lower it to 7.5 or so.
(use calculator)
your heavy doses of acid will lower your TA.

70-90 TA is the range you seek.

 

[planoattorney]

Thanks. I have always tried to keep Ph in the 7.5 area, it drifts up, I would lower, it would drift up. Last night I was not really planning on putting that much acid in the pool, I just started pouring without thinking about how much I would put in, but I did plan to add some Borax anyway, so it worked out in the long run. Worst case, I can add a little Baking Soda to raise it a hair and I have been increasing CYA very cautiously since that was the most obvious cause of past problems (ignoring operator error). The CYA is probably closer to 35 than 40, but the instructions said the "closest line".

Are you using bleach? If so, how much do you add per day and how big is your pool?

 

[Mr Bruce]

Wait until your pH goes over 7.8 to lower it. I used to do the same thing, trying to keep it at 7.5 thinking that was the "middle". My pool just really likes to be 7.7-7.8 with a TA of 50. I add 1/10th the acid I used to.

 

[7snorkel]

Your PH will always drift UP. Splashing, fountains, spillovers, and rain will cause it to go up. If your pool is still most days(no spillovers or fountains) you should see very gradual drifting up.
a good rule I've learned here is to add half the amount the Pool Math tells you. Wait a bit, re-test, and see if you need more.
Yes, i use bleach. 8 Jugs at Walmart (8.25%) nearly every trip i make. $2.94 a jug. Haven't seen the Green Monster once since I've start this method. i add 90 oz a day this time of year. 20K pool. lots of sun, though.
i add late evening after sun is off my pool. This way the pool has about 12 hours to sanitize without being compromised by sun.

I introduced my friend to this method and he's tickled to death that his pool now sparkles. He's 80 yrs old, smart as a whip, and re-loves his pool. took him a couple of months to wrap his brain around it, but he's so happy.
His pool is 22,600, but has more shade. 2ppm per day for him.


"A properly chlorinated pool will never see algae" -- Duraleigh