Pool Using Lost of Acid

[Great To Be Alive]

Hi All... Newb here. Just trying to get a handle on why my pool is using so much acid. Here are my stats:

• Constructed in Nov 2019... so only 4 months old
• Pebble Sheen finish
• Spec from builder shows 8500 Gal pool, but there is a Spa attached with overflow that runs all the time, and pool seems to respond as if it's a 10,000 Gal system from a chemical standpoint
• Salt just added 2 weeks ago, and SWG started early this week
• Hayward Omnilogic with HLChem sense and dispense system with Acid Feeder
• Numbers are: FC 1.1(0 combined), PH 7.8, TA 110, Temp 60 ish, CYA 87, Calc Hardness 275

My question is this: It seems like I'm constantly fighting high PH. I filled the Acid feeder with a mix of 1Gal of 31% HCL and 4 Gal of water, and the system has used all that in about 4 weeks. Do I just keep adding acid to the feeder to feed into the pool and not worry about it, or is this a symptom of another issue? I know new pools can have high PH for a while, but I'm suspecting some other causes.

My spa is set to always have some flow when the pump is running, and I've noticed my SPA bubbles when the pump is running at anything over 75% even when the blower is turned off... so I'm suspecting that may be driving PH up. Don't use the Sheer water features much at all. Tried running the pump at 50% instead and that seemed to help a bit, but still using acid.

Any help or suggestions would be appreciated. Thanks!

 

[bmoreswim]

A lot is a relative term. A pool needs what it needs to keep the pH in the 7.2 - 7.8 range. The amount is irrelevant. So give it what it needs to keep proper pH. That said, a new plaster pool, by it's chemical nature, requires more acid to keep rising pH down than an older pool. Also, low pH rises faster than higher pH. So running the range of 7.5 - 7.8 may work better than going down to 7.2. Yes, any bubbles will assist pH with rising.

This is unlike chlorine usage where higher usage may mean you have an algae problem.

 

[Newdude]

Welcome, and I couldn’t agree with your screen name more. The biggest step is finding your way here. Well done. Next is filling out your signature so everybody can see what you are working with. We have lots of plaster experts who will be along shortly to detail the reasons why your new shell is sucking up acid. It’s a process like anything else but somewhat normal and can take a few months like you’ve seen.

In the meantime, Have some reading to get you started . Start-up New Plaster - Trouble Free Pool

 

[scottts]

I notice you have an SWG. Here's my experience.

I have a gunite pool with a radiant fusion surface that's about 6 months old. At first it used acid a lot as you are experiencing. NOW it really only uses acid when the SWG runs, although when hades returns to the desert southwest in a month or two (that's what I call summer), I expect evaporation to greatly increase and acid demand to go up. I have an intellichem system and it only allows the SWG to be on at 100% (a major flaw in my opinion).

For some reason my pools chemistry basically uses acid (HCL) as the fedstock for making free chlorine (and hydrogren gas). Yes, I know there's more complicated chemistry in there but the net effect is when the SWG comes on in response to a drop in ORP the pH starts to rise nearly immediately and the intellichem starts dosing to keep it down. As soon as I turn off the SWG, pH normalizes and acid demand essentially stops. It can use a gallon of the 14% acid in 24 hours. This cycle drives down my TA so watch for that too.

So maybe your SWG also converting acid to chlorine and that's the demand you are seeing. Your 4:1 acid dilution is pretty high, you might try diluting to 2:1 to get more time between tank fills. I would also target 7.6 pH or even up to 7.8. Intellichem only allows a max set point of 7.6 so i'm stuck there.

 

[bmoreswim]

I saw decreased pH rise after the first year. But the timeframe varies for sure.

 

[bmoreswim]

I notice you have an SWG. Here's my experience.

I have a gunite pool with a radiant fusion surface that's about 6 months old. At first it used acid a lot as you are experiencing. NOW it really only uses acid when the SWG runs, although when **** returns to the desert southwest in a month or two (that's what I call summer), I expect evaporation to greatly increase and acid demand to go up. I have an intellichem system and it only allows the SWG to be on at 100% (a major flaw in my opinion).

For some reason my pools chemistry basically uses acid (HCL) as the fedstock for making free chlorine (and hydrogren gas). Yes, I know there's more complicated chemistry in there but the net effect is when the SWG comes on in response to a drop in ORP the pH starts to rise nearly immediately and the intellichem starts dosing to keep it down. As soon as I turn off the SWG, pH normalizes and acid demand essentially stops. It can use a gallon of the 14% acid in 24 hours. This cycle drives down my TA so watch for that too.

So maybe your SWG also converting acid to chlorine and that's the demand you are seeing. Your 4:1 acid dilution is pretty high, you might try diluting to 2:1 to get more time between tank fills. I would also target 7.6 pH or even up to 7.8. Intellichem only allows a max set point of 7.6 so i'm stuck there.

I do want to clarify so we are all on the same page...acid is not used by a SWG to create chlorine as noted above. There is some pH rise due to the hydrogen gas created as part of the reaction inside the salt cell, but it is minor.

The OP's issue (if you want to call it that) is just related to the curing plaster causing pH to rise more now than it likely will in time.

 

[ajw22]

New plaster + constantly running spillover + SWG is a recipe for a constantly rising ph in the pool.

The factor that you can control is not running your spa spillover all the time. Many of us set our automation to refresh the spa water by runningt he spillover once or twice a day for 15-30 minutes.

 

[ajw22]

I do want to clarify so we are all on the same page...acid is not used by a SWG to create chlorine as noted above. There is some pH rise due to the hydrogen gas created as part of the reaction inside the salt cell, but it is minor.

I think that SWG generated hydrogen gas aeration pH rise is being seen by @scottts ORP sensor which is feeding acid. That cycle is one of the reasons we don't recommend ORP controlled chemistry for residential pools.

 

[scottts]

I think that SWG generated hydrogen gas aeration pH rise is being seen by @scottts ORP sensor which is feeding acid. That cycle is one of the reasons we don't recommend ORP controlled chemistry for residential pools.

I've lurked here long enough to be aware that my observations don't 100% comport with the general theories at TFP. I understand completely the limitations of ORP. I've even changed my ORP probe to a gold tipped one to prevent hydrogen poisoning of the platinum one that came with the intellichem. However, I have done enough experiments, not using the ORP settings to drive the SWG, and research to know what I observe to be what is true for my pool. SWG use, no matter the ORP level indicated, uses acid voraciously in my pool. It may in others as well.

Not trying to be controversial.

 

[Great To Be Alive]

Thanks for all the replies and input. The pool plumber set up the pool so I can't turn the spa off unless I turn the sheer features on, which doesn't get me anywhere in the PH reduction efforts. Strange that the auto valve changes from "sheers and returns(set to off mostly)" to "floor cleaners and slight SPA overflow"... So unless I manually shut off the spa overflow I can't reduce the bubbling effect. I would have plumbed it differently.

Sounds like I shouldn't worry about the amount of acid the pool uses. As a side question... do I need to worry about the auto acid feeder coming through the floor cleaners, which is how it's set up? The recommended solution in the feeder is 1 part to 4 parts water... so it's already diluted. Then when it gets injected into the pipe it's immediately diluted as well, so I think I'm okay, but I tend to use it as a semi-automatic dispenser, and turn it off before we swim and an hour or two before the pump turns off so I don't have acid dispense right when the pump is shutting off. Curious about your thoughts on that.

Thanks again for the help!

 

[ajw22]

Post pics of your equipment pad and valves. Let’s see what the plumber did.

 

[Katodude]

New plaster, plus TA of 110, and a spillover = acid usage.

Test your fill water as well. Helpful to know what you are adding to your pool.

 

[Rattus Suffocatus]

If you read the Wikipedia article about SWCGs, it basically says that effectively the SWG uses acid to produce the Chlorine because to recycle the ions back to salt requires it. That is probably an oversimplification and I suspect many here might disagree. But at the very least it means acid demand will go up with a SWCG.

This is why I have held off on a cell for the pool up until now, but I am considering buying one once the water temperature is over 65F and I run through my liquid chlorine supply regardless. My pool was completed in September 2019.

The high TA Arizona water is a big driver of rising pH. Having aeration via the Spa is another factor.

Having new plaster is a factor.

I think you will see the TA drive down and the acid demand will stabilize, but we are in the environment that is... Well Rocky and mineraly... So expect the acid to always be needed. I am actually shocked that I am using so little in the pool, but after my water change in my detached spa I am using relatively a lot to get it stable again.

I would not worry at this point.