PH always, constantly drops.

[adnedarn]

Hello everyone! This question is for my work pool that I take care of at an apartment complex, not the pool in my signature...
13,000 gallons
bluish plaster
semi-public (about 20-40 swimmers a week I would guess... really not super busy)
Sanitizer 3" tabs trichlor

Current numbers:
FC 4
CC 0
TC 4
T/A 180
ph 7.5 (added 8 cups soda ash today to get here)
CH 500
CYA 320-380

I have been taking care of this pool for about 10 years, and every year, the whole swimming season, I am constantly adding Soda Ash. I buy it by the 50lb bag and go through a few of them for the swimming season (picked up my second bag today) I would say I add approx. 8 cups of soda ash every 5-9 days. The pool place I buy from finds it strange that I need so much of it, as normally everyone needs to keep on adding acid, not soda. My tap water is on the higher end of PH so it's not from that, although I try to do weekly unnecessarily long back washes (in attempt to keep CH and CYA down mainly).

Any ideas on making the PH more stable would help me, and since we're doing so well on my pool (even though mine is liquid bleach) I figured you all are my best chance of help.
Thanks!!
Andrew

 

[jblizzle]

Easy ... stop using trichlor.

The pucks are also why your CYA is such a ridiculously astronomical number (how did you even measure that high?)

 

[JasonLion]

Trichlor pucks add chlorine, add CYA, and lower PH.

 

[adnedarn]

No way I could go liquid chlorine without some automated system that the owner would never pay for. For some reason, I thought they took the PH the other way. Sorry I didn't double check that. Yeah, I knew that's why the cya was high... the fact that I found it impossible to keep cya low using those pucks even with heavy constant back washing is the main reason I'm doing liquid chlorine at home. I diluted pool water 1 to 3 parts tap... that's why I gave a range... I know it was only good for getting a glimpse of an idea of what it's actually at. That and CH were WAY higher when I first joined this forum (got a house with my own pool) and really learned about it... and when I started doing heavy back washing. The certification process doesn't care about any of these things that this forum teaches so well are essential.

Thanks for the answers, but I still don't get why I have this issue but all the other commercial places that the pool guy deals with don't have my issue... I guess they are busier and get a lot more splashing to raise the PH.
Andrew

 

[jblizzle]

Do you know that the other places use pucks? Some commercial places may have chlorine gas injection or SWGs and thus not have the pH dropping as much.

 

[adnedarn]

Yes, I deal at a local shop, but deal specifically with the commercial sales guy. I had checked if my chlorine consumption (by purchase schedule) was more that other similarly sized pools... (unrelated question then, but beneficial information now ) I buy the exact same brand and size bucket and it's less than most.

 

[chem geek]

Thanks for the answers, but I still don't get why I have this issue but all the other commercial places that the pool guy deals with don't have my issue... I guess they are busier and get a lot more splashing to raise the PH.

Bingo! Either that or their TA levels are higher. Remember that the TA reading includes alkalinity from CYA. Because of your high CYA, your actual carbonate alkalinity is only 67 ppm. That's the same as a pool with 80 ppm TA and 40 ppm CYA. If you were to raise your TA level higher, then it would reduce the amount of pH Up that you would use because the pH wouldn't rise so much, BUT anyone using Trichlor still needs to add either pH Up or Alkalinity Up to add back carbonates lost from carbon dioxide outgassing.

Let's say that the chlorine loss in this 13,000 gallon pool is 3 ppm FC per day since it's mostly from sunlight as the bather load is light. Then this would be around 5 3" 8-ounce pucks per week (does that sound about right?) and would lower the pH to 7.2 if there were no carbon dioxide outgassing and it would lower the TA by 15 ppm. It would require around 8 cups of soda ash per week to restore the pH if there were no carbon dioxide outgassing, but the TA would rise by 25 ppm and carbonate alkalinity would rise by 20 ppm, yet we aren't seeing that.

So the lack of TA rise from using the pH Up is a mystery unless your chlorine usage was actually much higher and you had carbon dioxide outgassing. Something doesn't add up here. Did you ever intentionally lower the TA by adding acid?

 

[Richard320]

I'm pretty sure that public pools require CYA to be less than 100. Some places even lower. The owner may have no choice but to install an automatic feeder or a saltwater system.

PS. Yep. http://library.municode.com/index.aspx?clientId=16119 Section 8.32.080 - Water quality standards.

C. Chemical Standards. All pools shall be continuously disinfected by an approved means which will maintain an adequate, readily measurable residual or disinfectant in the water. Whenever chlorine, or chlorine compound, is employed for pool disinfection, the amount of free chlorine residual in the water shall not be less than 1.0 P.P.M. or more than 5.0 P.P.M. at a pH of 7.0 to 8.0. Whenever chlorinated isocyanurate or isocyanuric acid are applied to the water for stabilization, the free chlorine residual shall not be less than 1.0 P.P.M. or more than 5.0 P.P.M. with a isocyanurate level of not more than 100 P.P.M. The total alkalinity must be between 60 and 180 P.P.M. The procedure for determination of free chlorine residual shall be by the DPD method or any of the other procedures outlined in the latest edition of Standard Methods for Examination of Water or Wastewater (APHA), or by other methods approved by the department.

 

[duraleigh]

Why not simply drain/refill to get CYA manageable and stay with the pucks----draining and refilling to control CYA. It is certainly not ideal but it let's you keep doing what you are doing under some better conditions.

 

[adnedarn]

Thanks for the answers, but I still don't get why I have this issue but all the other commercial places that the pool guy deals with don't have my issue... I guess they are busier and get a lot more splashing to raise the PH.

Bingo! Either that or their TA levels are higher. Remember that the TA reading includes alkalinity from CYA. Because of your high CYA, your actual carbonate alkalinity is only 67 ppm. That's the same as a pool with 80 ppm TA and 40 ppm CYA. If you were to raise your TA level higher, then it would reduce the amount of pH Up that you would use because the pH wouldn't rise so much, BUT anyone using Trichlor still needs to add either pH Up or Alkalinity Up to add back carbonates lost from carbon dioxide outgassing.

Let's say that the chlorine loss in this 13,000 gallon pool is 3 ppm FC per day since it's mostly from sunlight as the bather load is light. Then this would be around 5 3" 8-ounce pucks per week (does that sound about right?) and would lower the pH to 7.2 if there were no carbon dioxide outgassing and it would lower the TA by 15 ppm. It would require around 8 cups of soda ash per week to restore the pH if there were no carbon dioxide outgassing, but the TA would rise by 25 ppm and carbonate alkalinity would rise by 20 ppm, yet we aren't seeing that.

So the lack of TA rise from using the pH Up is a mystery unless your chlorine usage was actually much higher and you had carbon dioxide outgassing. Something doesn't add up here. Did you ever intentionally lower the TA by adding acid?

Sounds close, our puck demand may be a bit higher than that. So maybe sodium bicarbinate would be a better PH upper than soda ash since it would affect the TA more? I can only think of a handful of times that I've had to add acid to this pool- no I've never done it to intentionally lower the TA.
Andrew

 

[adnedarn]

I'm pretty sure that public pools require CYA to be less than 100. Some places even lower. The owner may have no choice but to install an automatic feeder or a saltwater system.

PS. Yep. http://library.municode.com/index.aspx?clientId=16119 Section 8.32.080 - Water quality standards.

C. Chemical Standards. All pools shall be continuously disinfected by an approved means which will maintain an adequate, readily measurable residual or disinfectant in the water. Whenever chlorine, or chlorine compound, is employed for pool disinfection, the amount of free chlorine residual in the water shall not be less than 1.0 P.P.M. or more than 5.0 P.P.M. at a pH of 7.0 to 8.0. Whenever chlorinated isocyanurate or isocyanuric acid are applied to the water for stabilization, the free chlorine residual shall not be less than 1.0 P.P.M. or more than 5.0 P.P.M. with a isocyanurate level of not more than 100 P.P.M. The total alkalinity must be between 60 and 180 P.P.M. The procedure for determination of free chlorine residual shall be by the DPD method or any of the other procedures outlined in the latest edition of Standard Methods for Examination of Water or Wastewater (APHA), or by other methods approved by the department.

Hmmm Interesting! I've taken the BS class a few times and don't recall ever seeing anything about that. I'll yank the book back out at work today and try to look for more info on your post above to see where the heck I've missed it.
Andrew

 

[adnedarn]

Why not simply drain/refill to get CYA manageable and stay with the pucks----draining and refilling to control CYA. It is certainly not ideal but it let's you keep doing what you are doing under some better conditions.

Well, I've mentioned that to the manager and she said we were going to put it out as a "have to" and see how that goes. The water bill is already pretty high, and I have to drop the watering on the plants to keep it low, which makes it hard already being in the desert. But we will add in the info that all this extra cost of chemicals is likely in connection with this "old" water and maybe that will win us an exception every now and then with the owner to do partial drains.
Thanks!
Andrew

 

[chem geek]

Sounds close, our puck demand may be a bit higher than that. So maybe sodium bicarbinate would be a better PH upper than soda ash since it would affect the TA more? I can only think of a handful of times that I've had to add acid to this pool- no I've never done it to intentionally lower the TA.
Andrew

No, I don't think you need to change away from pH Up when using Trichlor. I'm just puzzled that the TA didn't rise more with that usage even accounting for the Trichlor.

When you lower the CYA level then the TA will more accurately reflect the carbonate portion of alkalinity so you'll have somewhat better pH balancing, but will probably still need to add pH Up if you continue to use Trichlor. However, for every 10 ppm Free Chlorine (FC) added by Trichlor, it also increases Cyanuric Acid (CYA) by 6 ppm so at 3 ppm FC per day, that's increasing CYA by 55 ppm per month if there were no water dilution. You really need to look for an alternative chlorine source such as chlorinating liquid or bleach from a peristaltic pump (though that will be a lot of chlorine to carry) or using a saltwater chlorine generator.

 

[techguy]

Well, you could water the plants with the water you dump and use the plant water to fill the pool?

Don't know if that works or not but it's a fun idea.

 

[adnedarn]

Looking at my pool logs this morning, it looks like we are using way more chlorine pucks than I thought.... So I don't know... good news is, I checked and sure enough, in the very back of the book of my pool course book are some "information" pages, including a page on CYA and that limits are below 100ppm.... So I was able to use that to talk to the owner about the need of a drain, and more often drains as time goes by etc etc.... So staring tomorrow I will be draining the pool....
Thanks for all the help!


Just reviewed the "test" we have to take for certification, and it only asks what CYA is for... That's the only actual mention in the course and test booklet. You would think they'd mention the 100 PPM limit somewhere.... And the people that come to test and make sure everything is good never check that or even ask if it's been checked.

tech guy That sounds like fun but more trouble that it's worth... First off, I don't have hoses long enough to even begin that and I think a 3" hose would make it difficult to water things without digging them up. :lol:

 

[harleysilo]

I didn't participate in this thread, but that's great news! Glad you talked some sense into them, did they make you test CYA in front of them for proof?

 

[adnedarn]

The owner? No, he trusts what I said. Plus, he wouldn't want to have to pay for me to use my test kit (first one was free, more would cost. bwahahahhahahahaa)

I have my refill test stuff on the way... off topic, kinda.

 

[techguy]

You can rent 3 inch hose from HomeDepot along with a pump for not much at all. IIRC its about $40 for a 4 hour rent with as much hose as you need. Gets the drain job done in less than the minimum rental for me, including drive time. I had to drain 10,000 gallons to change my damaged liner. I was dry in less than 3 hours and used about 100 feet of hose.

 

[jblizzle]

Depending on how often you think they are now going to have to drain the pool to keep the CYA in check, they should really consider a SWG setup ... may end up more cost effective due to the reduced water replacement and reduced puck expense.

 

[adnedarn]

We own a pump and 3" hoses (a couple hundred feet worth) for when the back parting lot floods... He has it at home right now from draining his pool though (he shut it down, was tired of paying the bills) so he'll bring it in tomorrow.

I will mention a SWG set up to him... Never know unless I ask. This pool is old like mine, and my plaster guy said I shouldn't do SWG since the light fixture would likely decay away from electrolysis or whatever... I know this site talks about it being rare... but it still worries me.