Confused about PH

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setsailsoon

setsailsoon

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TFP Guide
Oct 25, 2015
5,128
Palm City/FL
Pool Size
25000
Surface
Plaster
Chlorine
Salt Water Generator
SWG Type
CircuPool RJ-60 Plus
Folks,

I've got all of 22 days of TFP pool experience and all is going pretty well... the pool is good on all the numbers and looks great. But I'm a little confused about PH. We get a LOT of rain here in Stuart Florida. For the last couple of days we've had a lot. I've noticed my PH gradually rises so I use 34.5% muratic to control. I searched all over the place on the net and these forums and the general consensus is that it's acidic... makes sense to me with the CO2. But just for the heck of it I tested the rain today. Wow! I get 8.0, double checked with my wife (she detects the red shades better than I do). I also used a calibrated meter and got 8.1. Is Florida rain just different? I'll post my recent test results below. The gap is a 10 day absence (I'm semi-retired consultant so that happens every month or two).

All comments welcome.

Best regards,

Chris

DateTACYAFCCCCHPHActions
31-Oct-15130<202002257.6
1-Nov-15130<201802257.7
2-Nov-15100<201402257.7
3-Nov-1590<201202507.5
4-Nov-1590807.5
5-Nov-1590702507.6
6-Nov-1547.8Addded 16 oz muriatic acid 31.45%
6-Nov-1580<20402757.46 hr after acid addition
7-Nov-1580<202.503007.6Added 1 gal 10% Cl
8-Nov-1514Added .75 gal 10% Cl, 10 oz 31.45 Muratic Acid, 6 oz trichlor
9-Nov-15Out of Town
10-Nov-15Out of Town
11-Nov-15Out of Town
12-Nov-15Out of Town
13-Nov-15Out of Town
14-Nov-15Out of Town
15-Nov-15Out of Town
16-Nov-15Out of Town
17-Nov-1590203.503008added 20 oz 31.45% Muratic Acid
18-Nov-1527.4
19-Nov-1527.5added 8 oz trichlor, tested after 6h w/pump FC 3, Ph 7.5
20-Nov-155
21-Nov-1580206.503007.7cut chlorinator back to 0
 
The rain water's pH has nothing to do with the pH rise of your pool. pH rise in pool water is completely dominated by carbon dioxide outgassing from the water. The chemistry isn't complex but there are a few reactions happening - CO2 outgassed from the pool water then the bicarbonate buffer (the largest component of TA) shifts so that it creates more CO2 in the water. The process of bicarbonate (HCO3-) converting to aqueous CO2 requires the consumption of a proton (H+) and thus increases the measured pH.

Rain water hitting the surface of your pool causes increase aeration of the water thus increasing the rate of CO2 outgassing. As well, all pool water is over-carbonated compared to atmosphere so there is a natural driving for for your pool water to outgas CO2 constantly. This is why when you cover your pool you can almost totally arrest the pH rise because there is no CO2 outgassing.

I do believe you that your rainwater has high pH. Rainwater pH can vary quite a bit depending on climatic conditions. However, unless your pool is overflowing with rainwater everyday, the pH of a few inches of rain should make little difference to your 12,000 gallon pool. If rain water dilution was substantial, pH would be the least of your chemical problems as your CYA and CH would be dropping like a stone.

- - - Updated - - -

BY the way, your CYA (stabilizer) is quite low. You should increase it up to a minimum of 30ppm. Are you keeping it low over the winter?
 
I am also in FL and find that a big rain will push my PH up. It is just something we live with so I keep MA on hand to push it back down.

I use my returns to roll the water if I want to push the PH up if it drops for any reason. It does it quickly so I have to watch it close.

Kim
 
Joyful,

Thanks so much for the comprehensive response and that makes a lot of sense. This is taking me back about 45 years but I do seem to remember ph = -log[H30]... so less hydroniums means higher PH. TFP chemistry is making more and more sense to this newbie. On the CYA I guess it's the fact that I do get a lot of rain, in two years here I've only added water once. That happened when I returned home and the pool was completely full from rain so I hooked up the hose to a valve downstream of the pump and just left it wide open a couple of days. Bad move... I learned all about letting the level drop too far and sucking air into the pump. But I did finally get to add a little water. Much of the time I have to drain out 3" per week but this time of year we only have to drain an inch every now and then. My FC consumption doesn't seem excessive and I'm guessing that's due to the screened in enclosure that really cuts down on the sunlight and wind on the surface. So I sort of ignored the low CYA while I learned about TFP chemistry and I focused on learning how to control FC with liquid (10%) and control the ph with Muratic. Now that I'm getting confident with that part (maybe overconfident) I'm adding FC with just trichlor until I get CYA up to at least the minimums. While I'm at it I'm now figuring out how to adjust the tablet feeder.... seems to be a little finicky. Once I get the CYA in order I'll switch back to 10% liquid. I really thought handling the gallon jugs would be a pain but I'm finding that it's no big deal to me. And I really like the underlying philosophy I have learned here of adding only what I need. Does this approach make sense to you or should I have a little more urgency about the low CYA?

Kim, thanks for the reply and I guess between the phenomenon Joyful mentioned plus our 8 pH rainwater we'll be keeping that muratic handy in the deck box. We got at least 2" today in a couple of BIG downpours. Thanks for the advice on small adds of muratic... I was shocked at how quickly it dropped with my last add of 20 oz... I think I'll go half that much next time.

Thanks to both of y'all for the thoughtful and helpful replies.

Chris
 
Chris do you have the bleach and MA in the same box?? If you do PLEASE go out right NOW and take the MA out of the box and put it in a different place that is well vented, away from anything that can rust.

MA and bleach/chlorine do NOT play well together! Well they do if you like things that go boom!

Kim
 
Hi Chris,
it seems you are getting the hang of things and learning. It's always nice to see that. Learning is what TFP is all about.

There is no urgency in getting your CYA up in your situation. And no harm in using the thrichlor tabs and then switch to liquid when you need to.
 
kimkats said:
Chris do you have the bleach and MA in the same box?? If you do PLEASE go out right NOW and take the MA out of the box and put it in a different place that is well vented, away from anything that can rust.

MA and bleach/chlorine do NOT play well together! Well they do if you like things that go boom!

Kim
Click to expand...

Kim,

Thanks!... I had them in opposite end of the deck box but moved the acid to a different container that's well ventilated... I had no idea they'd go boom! If that happened it would be the end of TFP for me... my wife would fire me and call the pool service.

Thank you sooo much!


Chris
 
Divin Dave said:
Hi Chris,
it seems you are getting the hang of things and learning. It's always nice to see that. Learning is what TFP is all about.

There is no urgency in getting your CYA up in your situation. And no harm in using the thrichlor tabs and then switch to liquid when you need to.
Click to expand...

Thanks Dave, It helps to know that y'all think I'm doing OK... well sort of. I think Kim averted a potential disaster with her previous post. That would have been just great... I'm just now getting comfortable with this then boom! If I didn't get anybody hurt I'd have been banned from pool care for life. Thanks again Kim!

Chris
 
Good deal Chris,

You're coming along fine, and I applaud you for not trying to bite off more than you can chew with regards to learing the chemistry. No need to make the learning curve steeper than it needs to be. Right?

I dont think Kim literally meant they will go boom. If there were to be an accidental spillage of both, and they mix, it won't explode. What hapens is that toxic chlorine gas is created and it's very dangerous. So, its always a good idea not to store them in close proximity for that reason.

if you do happen to accidentally mix them, and see a green or brown gas cloud rising....run upwind.
 
Okay so not go boom (I had no idea what it would do but knew it was bad to mix them) but toxic gas.......SCARY!

Good job moving them away from each other.

You are doing an awesome job learning. How are things going today? How does your pool look?

Kim
 

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Kim,

Boom or not I had them way too close and spill could have happened with very bad results. I made the change right after I read your post and I've told my wife about the mistake that a very smart pool lady warned me about.

Thanks for the follow-up and encouragement. The pool is looking great! Yesterday I vacuumed as it had been 3 weeks! The enclosure we have helps keep the dirt to a minimum but I had these ugly brown patches that must be very light dust. When I wave the brush over top of it it sort of looks like a miniature dust storm about 6" high off the bottom. Can't imagine where that comes from but there is still a good bit of construction around here. Anyway the pool looks better than ever!

Chris
 
Kim,

Wow, I haven't done an OCLT yet so I'll check. Sounds like a good thing to add to my testing as well. I'd sure hate to have an outbreak now. I have a consulting gig coming up in Texas and will have to leave the pool untreated for 5 days next Sunday so I want it to be in great shape before I leave.

Thanks for the help again!

Chris
 
Kim,

Great news, my wife Robin has agreed to do some of the simple tests while I'm away.

Keeping to the subject of this thread we've also found a way to hone our color test accuracy for pH. I bought a highly rated but very inexpensive meter and also bought some pre-mixed calibration fluid. I'm finding with this as our back-up we're getting pretty good at pH... the calibration is a pain and not something I want to do long term but it's a pretty cheap tuition so we can confidently rely on the color test long term. I'm also realizing we weren't all that bad before. I was off by a max of .2 and Robin was off no more than .1... I guess it's a female thing.

Again, many thanks for all your help.

Chris
 
Just a note, I see you have a spa on your pool as well. My own pH increases when we run our waterfall, as the water aerates. Our central FL rain seems to increase pH as well. Just our observation, maybe the spa bubbling is helping increase the pH as well.

Just my 2 cents
 
flipr said:
Just a note, I see you have a spa on your pool as well. My own pH increases when we run our waterfall, as the water aerates. Our central FL rain seems to increase pH as well. Just our observation, maybe the spa bubbling is helping increase the pH as well.

Just my 2 cents
Click to expand...

Yes, this is quite common and your intuition is correct. The bulk of your water's alkalinity comes from the bicarbonate anion (HCO3-). When you aerate the water, whether by spa jets, waterfalls, bubblers, spillways, etc, you force dissolved CO2 out of the water. Dissolved CO2 will also just naturally outgas as pool water is over-carbonated relative to atmospheric CO2. When the dissolved CO2 leaves the water, the bicarbonate behaves according to the following chemical reactions -

CO2(aq) + H2O <---> H+ + HCO3(-)

(Dissolved CO2) + (Water) <---> (acid proton) + (aqueous bicarbonate)

So the bicarbonate reacts with an acid proton to form water and aqueous CO2, i.e., the bicarbonate is trying to restore the balance of the CO2 lost from aeration. Since the reaction consumes a hydrogen ion, the pH goes up.

Almost all pH rise in pool water can be attributed to outgassing of CO2 from the water. If you turn off, or greatly reduce your aeration sources, and cover your water with a simple pool cover, you will see the pH in your water rise much more slowly than when it is uncovered.
 
Folks,

Thanks for all the great replies! The aeration makes a lot of sense. Water returns to the spa and then through two overflows to the pool all the time the pump runs. I run it from 9 am to about 5 pm to take advantage of the solar heating so I'm doing a lot of aeration. Joyful, I'm still trying to follow the water chemistry... so what happens to the H+ that is liberated? Does it combine with dissolved O2 until a new equilibrium is achieved... I guess there's a plentiful supply with my aeration. Sorry for the dumb water chemistry questions it's just been a LONG time and never was my strong suit.

Kim, next time I get the brown stuff on the bottom I'll try to get a sample and look at it under my old college microscope (if it still works). Pollen should be easy to spot and Robin says Hi back! and she naturally agrees...

Thanks again for all the replies.

Chris
 

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