pH just keeps rising and I'm using a lot of acid

[mkboudreau]

Hey Guys,

This is my first post, but I've been reading and learning here quite a bit.

My current issue/concern is that my pH seems to rise a LOT. I feel like I am putting 1-2 quarts of acid every day or every other day. I even put 1 gallon of muriatic acid in my pool the other day when pH jumped to 8 and 2 days later, it was already back to 7.9. I know that my salt water chlorine generator consumes acid. I also know that new plaster (4-5 months now) causes pH to rise. Is there anything I should be alarmed about? I thought it might have been normal when my TA was high >120, but I've worked really hard to get it down and it is now down to 70, but the pH rise is still there.

Latest measurements:
FC: 7.5
CC: 0
pH: 7.9
TA: 70
CH: 250
CYA: 60
Salt: 4200
TDS: 3740

Thank you in advance for any advice!

 

[jblizzle]

Welcome to TFP!!!

The SWG does not "consume acid". There are tiny bubbles that develop in the cell which effectively aerate the water which is what raises the pH.

I just plugged your numbers into PoolMath and your water right now is pretty aggressive and could be pulling calcium out of your plaster. This is due to your CH being on the low side and you lowered your TA. Both of these are fine, but you need to consider the CSI (see PoolMath). If all you did was raise the pH up to 8.0, then your water would actually be more balanced.

In areas of little rain, the CH will tend to rise just due to evaporation and topping off your pool from the hose. That is why I did not intentionally raise my CH from 150ppm, I just kept the pH higher to compensate. Now that my CH is 500ppm (3 years after fill), I have have driven my TA down to 50ppm and need to keep my pH lower to avoid calcium scaling in the SWG.

Have you discovered Pool School yet? Start with these:
ABCs of Water Chemistry
Recommended Pool Chemicals
Water Balance for SWGs

 

[JoyfulNoise]

One other thing you should do is raise your CYA to at least 70ppm or, even higher, to 80ppm. It seems counter-intuitive but, by raising your CYA (and your target FC as well to maintain the proper FC/CYA ratio) your pool will lose less FC each day to UV. This means you can likely run your SWG fewer hours each day and thus decrease your aeration a bit.

What are your pump run times and SWG % output?

 

[mkboudreau]

One other thing you should do is raise your CYA to at least 70ppm or, even higher, to 80ppm. It seems counter-intuitive but, by raising your CYA (and your target FC as well to maintain the proper FC/CYA ratio) your pool will lose less FC each day to UV. This means you can likely run your SWG fewer hours each day and thus decrease your aeration a bit.

What are your pump run times and SWG % output?

I am running my pump 4 hours on, 4 hours off totaling 12 hours on. SWG % only on for 6 hours total (separate timer) at 40% right now.

 

[mkboudreau]

Yeah, I've been watching my CSI as well and I actually lowered my TA lower than I was targeting. My one concern about raising CH is we've been getting a little bit of white crusty crystals around our tile, just under the coping. I was concerned that raising CH would not be a good thing. What are you thoughts on this?

Regarding my mention of SWG "consuming" acid... my understanding of the chemistry of the SWG is that the salt (2NaCI) plus water (2H2O) + acid (HCl) through electrolysis ultimately creates chlorine, salt and water, while bubbling off the hydrogen. the end result is the acid that was part of the initial input is gone and the result is the chlorine and the hydrogen that was bubbled off.... i'm sure "consume" isn't the correct term, it's just how i think of it.

 

[JoyfulNoise]

That's not quite right. The net reaction inside the cell when you consider the two half-cell reactions (anode + cathode reactions) is -

2H2O + Cl- --> HOCl + OH- + H2(g)

The chloride ion can come from any source (salt, muriatic acid, spent bleach, etc), in fact, most manual chlorination pool owners can't believe how high their pool salt levels are just from using bleach.

As well, when hypochlorous acid (HOCl) reacts with something (algae or organic molecule), the reaction is acidic in nature a produces a proton (H+). So, on balance, the chlorine production and disinfection process is pH neutral.

What causes the pH to rise in an SWG pool is the hydrogen gas bubbles aerate the water which liberates CO2. The release of CO2 gas from the water causes the bicarbonate alkalinity to shift equilibrium to correct for the loss of CO2. When bicarbonate (HCO3-) coverts to aqueous CO2, it consumes a proton (H+) in the reaction and that is what causes rising pH.

 

[mkboudreau]

great info.. thank you!

back to my original question: should i be concerned about how much acid i am having to add?

and then the follow on question from another post: will raising CH negatively affect what we are currently seeing with some white crusty crystals around the tile and coping?

That's not quite right. The net reaction inside the cell when you consider the two half-cell reactions (anode + cathode reactions) is -

2H2O + Cl- --> HOCl + OH- + H2(g)

The chloride ion can come from any source (salt, muriatic acid, spent bleach, etc), in fact, most manual chlorination pool owners can't believe how high their pool salt levels are just from using bleach.

As well, when hypochlorous acid (HOCl) reacts with something (algae or organic molecule), the reaction is acidic in nature a produces a proton (H+). So, on balance, the chlorine production and disinfection process is pH neutral.

What causes the pH to rise in an SWG pool is the hydrogen gas bubbles aerate the water which liberates CO2. The release of CO2 gas from the water causes the bicarbonate alkalinity to shift equilibrium to correct for the loss of CO2. When bicarbonate (HCO3-) coverts to aqueous CO2, it consumes a proton (H+) in the reaction and that is what causes rising pH.

 

[jblizzle]

I think you are adding too much acid because you are trying to keep your pH too low.

There will always be deposits on the tile due to evaporation. The higher the CH and the CSI get, the more likely you are to get more of a build up.

 

[mkboudreau]

My target pH has always been right around 7.7. The only reason I added 4qt when it hit 8.0 was because i was tired of adding 1qt - 2qt per day just to keep it at 7.7-7-8. Is this me trying to keep it too low??

Regarding the deposits... I'm hoping it is normal evaporation and that's all. My CH is fairly low right now and my CSI is negative, so that's more or less why I'm curious about the build up.

I think you are adding too much acid because you are trying to keep your pH too low.

There will always be deposits on the tile due to evaporation. The higher the CH and the CSI get, the more likely you are to get more of a build up.

 

[jblizzle]

You posted a pH of 7.5, the CSI says that is getting too low. I would keep it up between 7.8 and 8.0

 

[mkboudreau]

? My pH is listed at 7.9 in my first post. My understanding, and you all can correct me if I'm off, is that it'd be better to adjust my TA up a tad and my CH up a tad and keep my pH in the 7.6-7.7 range. That sounds more desirable than allowing my pH to be 7.9-8.0 and keeping my TA and CH low. With my constantly rising pH, I'm not sure how I'd keep it stable and not accidentally creep >8.0.

You posted a pH of 7.5, the CSI says that is getting too low. I would keep it up between 7.8 and 8.0

 

[jblizzle]

Oops, you are right ... I just saw the FC number.

Making the TA and CH and pH adjustments would result in the same CSI as if you just let the pH stay a little higher.

Having a higher TA would make the pH rise faster.
The pH rise is actually slower the higher the pH level, meaning it will rise from 7.5 to 7.7 faster than from 7.8 to 8.0.

So what if the pH does get a little above 8, your CSI would still be near neutral.

NOTE:
What I am describing is a bit on the advanced side of the chemistry. If this makes you uncomfortable, then raise the TA and CH and keep the pH lower to be "in the range", but I bet you end up using more acid.

 

[mkboudreau]

Good info.. thank you

So about the pH >8... I was under the impression that in general a pH <7 or >8 can cause a number of problems, one being eye/skin irritability. Is that more a function of CSI than just pH?

I am guessing that adding 1qt of acid every day is not too alarming to anyone since nobody has really commented on that being a bad thing as long as my CSI is near neutral. Am I understanding that correctly?

Last thing: any change borates might be worthwhile? from what i've read on other threads I may still consume the same amount of acid, but it should slow down the pH rise.


NOTE: thank you for this conversation. it really helps me to bounce all these questions off the community!

Oops, you are right ... I just saw the FC number.

Making the TA and CH and pH adjustments would result in the same CSI as if you just let the pH stay a little higher.

Having a higher TA would make the pH rise faster.
The pH rise is actually slower the higher the pH level, meaning it was rise from 7.5 to 7.7 faster than from 7.8 to 8.0.

So what if the pH does get a little above 8, your CSI would still be near neutral.

NOTE:
What I am describing is a bit on the advanced side of the chemistry. If this makes you uncomfortable, then raise the TA and CH and keep the pH lower to be "in the range", but I bet you end up using more acid.

 

[pooldv]

Borates would help stabilize your PH.

I am with Bliz, keep TA a little lower and PH a little higher.

 

[JoyfulNoise]

Borates can help but your plaster is fairly new so you may want to wait the full year before you start dumping in more chemicals. I waited a full year before adding borates so that I could know my pool water better.

Going back to my original post, I think you should increase your CYA and run at a higher target FC. The less you can run your SWG per day, the better off you will be. I know that with my SWG if I get down to 60ppm CYA or lower, I have to run my SWG noticeably more. 50ppm is my absolute floor. I was once at 45ppm (roughly below 50 on the scale) and my SWG was up at 80% output just to barely hold the FC where I wanted it. CYA really does matter a lot for SWG pools.

 

[mkboudreau]

Good suggestions... I think I will wait on the borates for now and will bump up my CYA a little.

It still bugs me that I am constantly adding acid... 1qt-2qts per day.

Borates can help but your plaster is fairly new so you may want to wait the full year before you start dumping in more chemicals. I waited a full year before adding borates so that I could know my pool water better.

Going back to my original post, I think you should increase your CYA and run at a higher target FC. The less you can run your SWG per day, the better off you will be. I know that with my SWG if I get down to 60ppm CYA or lower, I have to run my SWG noticeably more. 50ppm is my absolute floor. I was once at 45ppm (roughly below 50 on the scale) and my SWG was up at 80% output just to barely hold the FC where I wanted it. CYA really does matter a lot for SWG pools.

- - - Updated - - -

I hear you. It just bugs me that I have to add 1qt-2qt of acid per day - even to keep pH at 7.9.

If I understand CSI correctly, bumping up CH would allow me to keep TA where it is ~70 and move pH down a little. Right now I'm at 250ppm for CH, so I have some room to move it up. Any issues with that? Sorry if it's a stupid question.

Borates would help stabilize your PH.

I am with Bliz, keep TA a little lower and PH a little higher.

 

[chiefwej]

New plaster combined with a SWG always has very high acid demand. You will see that slow down over time. In the mean time watch your CSI. You don't want to get it too low and damage the plaster or too high and have scale. The lower the pH you try to maintain, the quicker it will creep up. The key is maintaining a CSI near zero.