Chlorine usage high. Again

[A_kraker99]

Okay... I have posted about this before but now I am calculating my chlorine usage at about 4.1 PPM per day. I go through just over 4 gallons of 12.5% per week! This just seems really high to me. I passed the overnight loss test and CYA is at 50 so what’s the deal?
I see people at the pool store buying 1 case at a time. I go there and load up 6 cases that only lasts about a month.

 

[Newdude]

Dropping the CYA by 10 to 40 will lower your additions 19 oz a day, which would add up considerably. You are pretty far north and probably don't need the higher CYA.

 

[A_kraker99]

Dropping the CYA by 10 to 40 will lower your additions 19 oz a day, which would add up considerably. You are pretty far north and probably don't need the higher CYA.

How would that lower my additions? Doesn’t higher CYA protect it from being used by the sun?

 

[JimMarshall]

Hey I recognize you! Lol

additional questions, how long has it been since you passed your OCLT? And did you pass with flying colors or just barely pass? Have you checked all the places organics could be hiding? Drain covers, skimmer necks, light niches, etc?

mans have you checked and double checked your CYA test? How are you performing the test? It’s fairly common to test this level as higher than it actually is.

 

[Newdude]

How would that lower my additions? Doesn’t higher CYA protect it from being used by the sun?

You would drain 20% and refill. CYA is not naturally in any fill or rain water. You are correct that its needed to protect the FC from the sun, but 50 is a tad high for a liquid chlorine pool. Warm climates with high demand may need to go there, but you are much different than San Diego. In your case a 50 CYA needs 77 oz of 12% to gain 4 PPM, but only 58 oz at 40 CYA.

 

[JimMarshall]

You would drain 20% and refill. CYA is not naturally in any fill or rain water. You are correct that its needed to protect the FC from the sun, but 50 is a tad high for a liquid chlorine pool. Warm climates with high demand may need to go there, but you are much different than San Diego. In your case a 50 CYA needs 77 oz of 12% to gain 4 PPM, but only 58 oz at 40 CYA.

You’ll need the same number of ounces to add 4ppm whether the CYA is 10 or 100. I think what you’re trying to say is that the target number is lower so you won’t have to add as much to get to the target..... but that won’t help the chlorine need at all if his pool still needs 4.1 PPM per day

 

[Newdude]

You’ll need the same number of ounces to add 4ppm whether the CYA is 10 or 100.

Not according to pool math. It makes a difference.

 

[PoolNewb2020]

Not according to pool math. It makes a difference.

I don't know. My pool math apps says I need 36oz to go from 6 to 8ppm regardless of CYA level I enter.
Also, when you go to the Effects of Adding section in the app, for FC there is no CYA level required to be filled out in order to calculate FC raise.

 

[A_kraker99]

Hey I recognize you! Lol

additional questions, how long has it been since you passed your OCLT? And did you pass with flying colors or just barely pass? Have you checked all the places organics could be hiding? Drain covers, skimmer necks, light niches, etc?

mans have you checked and double checked your CYA test? How are you performing the test? It’s fairly common to test this level as higher than it actually is.

it’s been about a month since the last OCLT. I think I lost around .8 PPM overnight.
I really don’t have a lot of spots for organics to hide. Just the 2 main drain covers maybe? Could algae under those really use up that much chlorine in 1 day though? I can check them. Not sure if the covers just pop off or not.
I use the procedure on this site to test CYA. I have always been Leary of this test. I am pretty certain I am around 50 though.

 

[Newdude]

I don't know. My pool math apps says I need 36oz to go from 6 to 8ppm regardless of CYA level I enter

If it is set to SWG in settings the CYA doesn’t change the ounces of bleach needed. When I configure my user settings to be like OP’s, it does change the amounts needed based on CYA. Probably because If you have a SWG (or the app thinks you do) the liquid bleach is a supplement and not sole full dose. Maybe it’s a glitch. I dunno. @Leebo, @mknauss what do you guys think ?

 

[mknauss]

I get 36 oz in all modes. Of 12.5% in 18000 gallon pool. For 2 ppm FC rise.

 

[Psycho1122]

OP, can you confirm that you are working with a true 12.5% CL? Even CL a month old stored indoors can loose potency.

 

[CrystalRiver]

No matter how I change my settings, it always says the same amount is needed for the same rise in FC.

CYA does not change the chlorine levels. High or low CYA, adding a certain amount of chlorine will always produce the same rise in FC levels. The only thing CYA changes is how quickly that FC gets burned off by the sun, and effectiveness (hence FC/CYA chart).

 

[Newdude]

I get 36 oz in all modes. Of 12.5% in 18000 gallon pool. For 2 ppm FC rise.

Did you turn off the SWG in user settings ? Or do I have a bad version of the app ?

 

[mknauss]

I have multiple pool types set up in my app. All types showed the same amount. Check your data.

 

[JimMarshall]

Did you turn off the SWG in user settings ? Or do I have a bad version of the app ?

Just for S&G I went in and changed my sanitizer source to a SWG.
It still tells me I need 2 quarts, 3oz to add 4 ppm to my 13000 gallon pool.

 

[Newdude]

Check your data

On vinyl setting it changes the amount of needed LC based on CYA. Plaster and FG it doesn’t. So it’s a app issue. I’m on version 335 which should be current from 1 month ago

apologies for hijacking @A_kraker99.

 

[Chasarms]

4 ppm per day is on the high side of normal. Many people on this forum report such losses. I have as much confidence as anyone can possibly have based the wisdom of this forum and my test results that my pool is quite healthy, yet I lose about 4 ppm of FC. My pool is fully exposed to the sun all day and naturally heats to the low 90s at times.

Higher CYA does not increase chlorine demand. It does adjust the target number upward, but that is a one-time addition. It actually reduces chlorine demand. For example, if you are at 30 CYA with a target of 3-6 FC, and lose three ppm per day, in a week you will have added 21 ppm. If you jump to 50 CYA and a target of 6-8, it's a one-time addition of 3 ppm, but if the daily UV loss drops to 2.5, you're 0.5 ppm ahead after only seven days. Make sense?

In my very limited experience, there are diminishing returns on chlorine protection and CYA. The difference of jumping from 30 to 40 in my pool was pretty noticeable, probably close to 1 ppm per day. The effects of jumping from 40 to 50 were far less obvious. As usual, it is a trial and error process.

 

[Psycho1122]

I found the same result with my conditions. With pool on north side of house and shade sails, I loose 3 ppm per day (June - Aug.) at 40 ppm CYA. 30 CYA is definately too low and the difference between 40 and 50 is negligible.

 

[A_kraker99]

Thanks guys. My pool does get a lot of sun and this time of year I don't have a solar cover on it (if that blocks UV). Should I be concerned with the OCLT loss of .8 the last time I did it?
I also wonder if my darker liner has anything to do with burning off chlorine quicker. Higher temps near the liner causing increase chlorine usage maybe? Just a thought