Heavy rain resulted in very low PH, should I correct?

[ganselmi]

Hi guys.

First of all Happy new Year !

I have a brand new vinyl pool with SWG.

During the summer I always had to decrease the PH using muriatic acid.
My average values were:
FC 3
PH 7.6 (I've had to add acid twice/week to maintain this level )
TA 125
CH 250/300
Salt 3.400
CYA 50
Water temperature about 82F (28C)

A few days ago I've decide to switch the SWG bypass, empty the SWG cell and move to bleach to control FC, this because I'd like to preserve the cell and because the low clorine demand during the winter.
This spring/winter We are having heavy rain and the spring water we use for the swimming pool was heavily diluited and PH dropped down sensibly, today I've got the following value:

FC 5 (it increased despite I've reduced the pump/SWG time from 6 hours this summer to 1,5 hr in the past month)
PH 6.4
TA 80
CH 100/250
Salt 2.000
CYA next to zero
Water temperature about 50F (10C)

Should I increase PH ? What do you recommend for it (backing soda, diluited caustic soda, aeration .....) ?

Should i correct any other value?

Thanks for you advise !

Giorgio

 

[PoolGuyNJ]

I would add some pH Increaser like dense ash mixed in a 5 gallon bucket. The low pH will cause corrosion and pitting to anything metal such as a heat exchanger or metal/chrome as often found on light fixtures, rails and ladders and escussion plates.

If you have a heater and are not using it, dropping the pH from your normal of 7.5 in season to 7.3 will keep the sanitizer at near peak levels and help prevent scale. While it doesn't seem like a lot, it does have some benefit. Your alk level is fine so adding baking soda shouldn't be needed.

Running without CYA will shorten your salt cell's life. The cell will need to create more meaning it is working harder.

When I can, I tell my customers to bring the cell in the house in the winter. In my area, the metal plates and the coating act as a bi-metalic strip. The metal can expand and contract more than the coating and that weakens the coating. This is one of the reasons Pentair has the blank fillers available.

Scott

 

[polyvue]

FC 5
TA 80
CH 100/250
Salt 2.000
CYA next to zero
Water temperature about 50F (10C)

Should I increase PH ?
What do you recommend for it (backing soda, diluited caustic soda, aeration .....) ?

Hello Giorgio,

Considering that in the past you've had to add acid regularly to keep the pH in check, a pH reading of 6.4 is a dramatic development. It's possible that you've added a little too much muriatic acid recently and it will revert to mean over time but I think that a measurement of 6.4 is far too low and increasing it should be a priority.

Scott (PoolGuyNJ) gave you some solid recommendations. I don't know if it's possible to get your water balanced with a pH of 7.3 -- I think it should be higher and scaling really isn't an issue here. Right now you can't count on the SWG and long pump times to steadily increase the pH. Besides the treatments you've mentioned, you could add Sodium Tetraborate (20 Mule Team Borax) to increase pH or Sodium Carbonate (soda ash -- aka washing soda). Baking soda, as Scott suggested, isn't the best solution; it won't raise pH very much. Aeration takes too long.

I'd recommend that you boost the pH right away to at least 7.3 with soda ash or caustic soda. The Pool Calculator indicates a need for rather hefty quantities of these chemcials (5 lbs+ soda ash -OR- 2 lbs+ caustic soda) but it would be prudent to take a fairly conservative treatment approach by adding only one-half (or less) of the suggested quantity. Then test the pH and TA again after a few hours of pumping/filtering to determine if you need to add more or not. Don't want to overshoot the goal.

 

[JasonLion]

I would double check the PH reading before doing anything else. The most common PH tests only go down to 6.8 or 7.0. Because of that, a reading of 6.4 is suggestive of testing errors. There are just a few PH tests that go down to 6.4, which test kit are you using?

 

[ganselmi]

Thanks guys,
I've really appreciated your prompt answer.
I'm still wondering a similar PH decrease reason, the last time I've added acid was a couple of weeks ago after having had a PH of 8.2, and I've added 36oz (1000 ml) of 30% muriatic who decreased PH till 7.4 that looked great to me, then after 2 weeks of heavy rain, where additional diluition should have been occurred as well, without SWG running, I've got 6.4!
May the missing bleach produced by the SWG have plaied a role?

I was expecting a similar answer and I'll immediately apply your recommendations.
Borax is not easy to get over here but I can get caustic soda in every store, I'll start with a small quantity diluited with water to understand how much will increase the Ph then calculate the needed one in order to get 7.3.

Also thanks for the recommendation to store my SWG cell, because while it is not actually too cold, we can get sometime till 21F (-6C) in January and February.

I'll keep you posted with the progresses.

Giorgio

 

[polyvue]

I was expecting a similar answer and I'll immediately apply your recommendations.

I think we all posted at about the same time so you may have missed Jason's comment above. Please consider testing again before you add any chemicals. Thanks, Jason, I totally missed this.

 

[ganselmi]

Just realized that we've have written at the same time with Jason

Yes, a wrong PH reading can be definitively an option, I use a digital PH meter which is accurate but may have suffered from the temp decrease requiring a recalibration.
The actual reading has been done using Acquacheck strips (reading from 6.2 to 8.4) and the PH meter after recalibrating it, now they provide the same reading.

May be that 2 weeks ago the 8.2 reading was not accurate and adding the muriatic may have reduced the PH while not needed.

I would love using the TF100 or K-2006 test kits mentioned in the forum that seems to be very reliable, but they are not available in Europe and none ship them from the US, here we can only find the test strips or basic OTO/Phenol test, but none of them shows CC and the strips are not so accurate. I've found some electronic photometer kit but definitively too expensive (about $ 900).

 

[polyvue]

May be that 2 weeks ago the 8.2 reading was not accurate and adding the muriatic may have reduced the PH while not needed.

That's very likely. Not sure how often one needs to calibrate a digital meter but it certainly presents a potential hazard to accurate water testing and treatment. Sometimes, simpler is better. Having at your disposal a drop test kit with phenol red pH and FAS/DPD chlorine will improve the odds a bit.

I would love using the TF100 or K-2006 test kits mentioned in the forum that seems to be very reliable, but they are not available in Europe and none ship them from the US, here we can only find the test strips or basic OTO/Phenol test, but none of them shows CC and the strips are not so accurate. I've found some electronic photometer kit but definitively too expensive (about $ 900).

EDIT - Sorry, I was mistaken. Dave sent me a Private Message (PM) earlier today correcting my false assumption. For now, at least, TF Test Kits does not sell test kits outside the US (50 states.) If anyone else knows a reliable source that sells Taylor K-2006 test kits to international markets, please post back. A number of folks have expressed interest.

Please DISREGARD the following paragraph. - END EDIT -

Perhaps I'm mistaken but I think TF Test Kits does ship product to Europe. See chem geek's comment on this here. The company's current web site is amateurish (IMO) but the test kits, judging from the remarks posted on this board, are on par with the residential kits available through Taylor Technologies. Try sending an e-mail [email protected] or contact them by telephone 01 (919) 528-1104.

• Edited by polvue on Sunday, January 3, 2009 2:55 PM Pacific Standard Time.

 

[ganselmi]

Today I've bought what I think you call soda ash (sodium carbonate) that I feel safer to manage compared to caustic soda.

Before to add it to the pool, I've repeated the PH test using red phenol and I've got a surprise to see PH 7,2 ??????????
At this time I don't know what to think, just a natural PH raise from 6.4 to 7.2 in only 2 days?
Apparently the only difference was that yesterday we had a windy dry day, while the previous ones were extremely humid.

I've added just 1lb of Solvay soda (500gr) and after 2 hr the PH was measured at 7.4 looking great to me.

Because I was not trusting the tests anymore, I've played at the chemistry set, I've taken 4 glasses with bottled natural drink water that it is published to have PH 5,9, house's water, pool water before to add the solvay soda and finally pool water after adding the solvay soda.
Using the electronic PH meter I've measured respectively the following values: 5.9 - 7.5 - 7.2 - 7.4
Using the red phenol test I've measured respectively the following value: very low (yellow), 7.4 - 7.2 - 7.4

All the test have been repeated twice both with the electr. ph meter and red phenol.

Looking to those value it seems that the electronic ph meter works well and it is more accurate than the red phenol test, especially for the low ph values.

But it does not answer to my question, what happened past week?

 

[duraleigh]

The phenol red for measuring pH is an industry standard and is very reliable and repeatable. I would trust the phenol red before any other test.

 

[ganselmi]

The phenol red for measuring pH is an industry standard and is very reliable and repeatable. I would trust the phenol red before any other test.

I 100% agree with you, my test was only to be able to understand what's was wrong in my pool during the past week.
Initially assumed a wrong measurement but this was not the case, I had a Ph 6.4 past week (measured both with red phenol and electonic ph meter for a double check) then after 2 days came back to 7.2 (measured both with red phenol and electonic ph meter for a double check) and nothing have been done meanwhile.

 

[JasonLion]

The PH will go up over time because of CO2 outgassing. Normally this process is fairly slow, however the lower the PH the faster it will go up. With a starting PH of 6.4 the process can be very rapid. It is plausible that your PH went up over a couple of days given your low starting PH, especially if there was a source of aeration (rain, SWG, fountain, waterfall, etc).

In your original post, you mentioned that the TA had been 125 over the summer, but recently it was 80. If you used the same amount of acid to lower the PH as you had been using during the summer, it would have had a much larger effect on the PH because of the lower TA level. Did you take that into account, ie use a smaller amount of acid, when lowering the PH?

 

[ganselmi]

The PH will go up over time because of CO2 outgassing. Normally this process is fairly slow, however the lower the PH the faster it will go up. With a starting PH of 6.4 the process can be very rapid. It is plausible that your PH went up over a couple of days given your low starting PH, especially if there was a source of aeration (rain, SWG, fountain, waterfall, etc).

In your original post, you mentioned that the TA had been 125 over the summer, but recently it was 80. If you used the same amount of acid to lower the PH as you had been using during the summer, it would have had a much larger effect on the PH because of the lower TA level. Did you take that into account, ie use a smaller amount of acid, when lowering the PH?

This seems to be fitting with the recent combined events such as missing SWG and heavy rain.
Regarding the TA change I think it is more related to the rain water diluition, I had 125 this summer but while only using the spring water from my water well that has high TA and CH, the rain water should have a low TA because of the low mineral content, I'm I wrong?
When having to correct the PH level I've always used the pool calculator, I'm confident to have used the right quantity and I use to check and correct the PH at least once a week.
To give you an idea, over the past 2 months, because of the water diluition, the salt level moved from 3500 to 2000, about 180 lbs of salt lost in two months that if I'm not wrong (used the pool calculator for it) means about 6000 gallons of rain water spilled in the pool.
Yes I'm definitively wondering about dosing small quantities of acid, i.e. using a peristaltic pump to inject very limited daily quantity of acid.
As far as I've read in the forum this should help maintaining limited PH fluctuations but I should evaluate and set the summer and winter average acid consumption 'cause they should be different, at the moment I've seen that I'm using about 1/3 of the summer quantity (34 Oz vs 12 Oz).
I was wondering to use a peristaltic or pulse pump in conjunction with a dedicated timer, i.e. to run for a maximum of xx minutes at every filter pump run (I only want to inject acid when the pump is running).

 

[ganselmi]

Finally I've got the evidence !

I've put a container in order to collect some rainwater fell during the past day (1.5" in 24 hours) and tested its values getting the following results:

TA 0 (Zero, justifying my TA drop from 125 to 80)
PH 6.4 (finally got the reason for my sudden PH decrease)

So the reason definitively was the very high dilution that my pool's water got from (I would say acid) rainwater.

I'm missing summertime.....

 

[JasonLion]

When the TA of added fill water is very low, it hardly matters what the PH is, it will have very little impact on the PH of the pool. Think of TA as the ability to hold the PH when mixed with other water. The TA of the pool is much higher than the TA of the rain, so the pool holds its PH, while the rain has its PH converted to the PH of the pool. There will be some very slight change in PH from the rain, but with rain TA around zero it will be difficult to detect. The rain will also lower the TA by dilution, but that will take a very large amount of rain to have any significant effect.