HELP! Connecticut Pool is Eating Chlorine

[Naplespool]

My daughter in Connecticut has a 22,000 gallon plaster pool, constant speed pump, cartridge filter, gas heater. After opening the pool this year, she said the water had been crystal clear but the chlorine reading using strips was low, less that 1 ppm. She went out and got the Taylor K2006 FAS/DPD kit. That confirmed the very low chlorine level, less than 1 ppm. The pool chlorine has been maintained for several years with Trichlor tablets.

Because of the low chlorine this spring, they have been adding sodium hypochlorite (12.5%) regularly to try and boost the chlorine level, to no avail. And let me add again, in her words, the pool has stayed crystal clear. Over the past week they added several gallons of 12.5% chlorine and have seen chlorine as high as 18 ppm at night, 10 ppm by the next morning and 0 ppm by the end of the day.

The K2006 measurements are:

FC: As explained above
CC: 0.5 ppm
PH: 7.4
TA: 110
CH: 240
CYA: 65 ppm (using test kit, her first measurement of it), 100 ppm according to a check by her pool store, based on using Trichlor I estimate its over 100.

She hasn't had time yet for a proper SLAM and rightly wonders if there could be so much algae in a clear pool, and that the chlorine is being consumed at the rate of gallons of 12.5% sodium hypochlorite per day. One more thing, they are vacuuming debris from the bottom of the pool (dead algae I"m guessing).

My explanation for what's happening is that a high but not visible level of algae is consuming the chlorine, and that the >100ppm CYA is keeping even 4-5 gallons of chlorine from eradicating it.

What other explanations are there for her situation, and if none, is the first step to drain half the pool and get the CYA down?

 

[duraleigh]

CYA of 60-70 is not unmanageable. Is there a reason your daughter won't post here? Only a few members bite and we keep them on a leash!

 

[Naplespool]

I think she will eventually post but she's got a heavy work schedule.

There has has also been a lot of tree droppings in the pool.

The real question, is there anything to do here other than double-check CYA, get it to a reasonable level and then follow a full SLAM process?

 

[duraleigh]

If her test reported 65 ppm, why do you think it is higher?

 

[Naplespool]

Three reasons: the CYA test isn't easy the first couple times you try it, her local pool store measured it at 100, and a full season of chlorinating with Trichlor adds about 220 ppm of CYA, so it's not hard to believe that it's 100 or more even with a partial winter drain. If it's as high as 100, SLAMing gets difficult, right?

- - - Updated - - -

Still wondering though, is there any other explanation for the rapid chlorine depletion other than it's oxidizing algae and blown-in organic matter?

 

[pooldv]

We don't value pool store test results at all. Relatively high levels of rainfall in FL will dilute the CYA level enough to make me thing 65-ish isn't out of the realm of possibility. It might be off 10 or 15, but I wouldn't think you would be off any more than that as a CYA test newbie. I will say that I trust that 65 ppm number, although I would round it up to 70, more than any of the other two reasons.

Nope, nascent algae blooms is by far the #1 reason for suspiciously high FC consumption. And low CYA would be the next most common reason.

 

[Naplespool]

Thanks. Agreed on the pool store numbers. This is my daughter's pool and it's in Connecticut, the amount of winter rainfall added about 1/3 to the pool water.

She's going to retest tonight.

 

[pabeader]

From what you have posted, it looks like a loss of 8 ppm overnite? That points directly to something organic in the water. It might be hiding in stairs, behind lights or other things in pool. Also, clear to some folks would to cloudy to others. For TFP, 'clear' means tell heads or tails on a coin in the deep end.

 

[duraleigh]

One of the tenants we teach is to trust your own testing......you both should do that.....time and again it is the most correct.

Only two things consume chlorine....organics in your pool and sunlight.....there is nothing else.

 

[Naplespool]

Thanks. We are now trusting our own results. Again, we are in Connecticut, not Naples, FL.

Test kit is K2006

CYA several days ago was measured at 65 ppm. TA 110. CH 240 PH 7.4.

Here are Monday night 8 pm measurements:
CYA 80 ppm
FC 15 ppm
CC 1.0

Tuesday 6 am
FC 14.0

Tuesday 6 pm
FC 1.0 ppm

13 ppm chlorine loss in 12 hours!!!

It was sunny and in the 70s all day Tuesday, but since the OCLT was only 1 ppm, we're thinking it's not algae.

Since the CYA is between 65 and 80, we're thinking it's not sunlight that's consuming the chlorine.

Is it pollen?

At 80 ppm CYA a SLAM is going to require holding FC at 30. Should we start the SLAM or drain some water?

 

[domct203]

You can't test CYA at 8:00pm, nor on the cloudy, rainy days we have been having here in CT.

CYA needs to be checked outdoors on a bright sunny day, ideally around mid day when the sun is high. Keep the sun at your back and hold the view tube in front of you in your shadow, about waist high.

Right now my pool is at 50ppm CYA (as I prepare to switch to a SWG) and I'm only losing 2ppm in 24 hours. My pool is under two trees and gets a lot of organic debris in the spring.

It is puzzling that you show only 1ppm loss overnight, but 13ppm during the day.

Either way, all indications lead to a proper SLAM, but you need to get the CYA testing correct first.

 

[Swampwoman]

Naples, you'd asked if there's anything else that could consume chlorine except algae. While 95% of the time it is "sunlight and algae" chlorine also oxidizes or breaks down bacterial contamination and other chemicals such as pesticide overspray, etc.

So it really doesn't matter WHAT the chlorine is fighting...because its likely something you don't want in the pool. The solution is to SLAM Process to oxidize whatever is causing the high chlorine diet

I hope that makes sense. I don't want to see you drag this out over the mere lack of visible algae when either way the water needs oxidizing Slamming to get to normal baseline behavior is the sensible approach because even if you don't have algae now, the inability to hold chlorine will get you there in short order!

 

[Naplespool]

You can't test CYA at 8:00pm, nor on the cloudy, rainy days we have been having here in CT.

CYA needs to be checked outdoors on a bright sunny day, ideally around mid day when the sun is high. Keep the sun at your back and hold the view tube in front of you in your shadow, about waist high.

Right now my pool is at 50ppm CYA (as I prepare to switch to a SWG) and I'm only losing 2ppm in 24 hours. My pool is under two trees and gets a lot of organic debris in the spring.

It is puzzling that you show only 1ppm loss overnight, but 13ppm during the day.

Either way, all indications lead to a proper SLAM, but you need to get the CYA testing correct first.

We understand that the best method is bright light, but I don't thing you're suggesting that the 80 reading of cya is less than 30 are you?

We are struggling to understand the 1 ppm overnight and 13 ppm during the day.

Naples, you'd asked if there's anything else that could consume chlorine except algae. While 95% of the time it is "sunlight and algae" chlorine also oxidizes or breaks down bacterial contamination and other chemicals such as pesticide overspray, etc.

So it really doesn't matter WHAT the chlorine is fighting...because its likely something you don't want in the pool. The solution is to SLAM Process to oxidize whatever is causing the high chlorine diet

I hope that makes sense. I don't want to see you drag this out over the mere lack of visible algae when either way the water needs oxidizing Slamming to get to normal baseline behavior is the sensible approach because even if you don't have algae now, the inability to hold chlorine will get you there in short order!

Thanks. At 80 ppm CYA we need to get a stock of enough bleach to hold 30 ppm till our SLAM is done. And find the time among work and kids schedules. Since it's a big commitment we just want to make sure it is the correct step.

 

[domct203]

We understand that the best method is bright light, but I don't thing you're suggesting that the 80 reading of cya is less than 30 are you?

I am suggesting nothing more than the fact that your CYA test is inaccurate due to improper lighting.

The solution is still the same, SLAM, but you need an accurate CYA level to know the proper SLAM FC level.

 

[Naplespool]

I am suggesting nothing more than the fact that your CYA test is inaccurate due to improper lighting.

The solution is still the same, SLAM, but you need an accurate CYA level to know the proper SLAM FC level.

Got it, thanks, I agree. A wrong measurement means either too much chlorine is used and wasted, or there isn't enough chlorine for the SLAM to be fully effective.