Stumped with Massive Chlorine Loss

[kenn_00]

I’ve been successfully maintaining my pool with the TFP method for 7 years. But, I’m stuck this last few weeks and I hope someone can help.

I refilled my pool about 3 months ago. Got borates in there, got CYA to 60 (I’m in Arizona), got the alkalitnity where I wanted it (50-60 range), and all was well with chlorine loss at about 1.5ppm per day.

Then I missed a week and Chlorine got to 0 for a day or two. No visible algae. The pool looks great. But, it started eating a lot of chlorine. So, I decided to SLAM it. I’m now at 10 days of keeping the chlorine level over 20ppm and it’s still eating through 10-12ppm per day of chlorine (2-3 gallons a day in my 20,000 gallon pool). I don’t know what to do. I can’t keep putting $10/day of chlorine in this thing.

Any suggestions? Much thanks.

 

[Richard320]

Time to recheck things. Is the CYA still at 60? If it broke down somehow to 20 or less, you'd lose almost all your chlorine in a few hours. Have you tried the Overnight Chlorine Loss Test? That'll tell you if it's algae or sunlight that's stealing all your chlorine.

Could there be algae lurking behind the light or inside ladder rails or beneath steps?

 

[ship of fools]

Shock level for CYA of 60 is 24ppm. I would keep it at or above 24 and see if things improve.

 

[proavia]

Check behind the pool light, in and around any ladders and also the weir door for signs of algae. Lots of nasties can hide in those places.

Fill out your signature with your pool, equipment and testkit. This helps us to know a bit about your pool without needing to ask each time.

 

[kenn_00]

Thanks all. No stairs, behind light is clean, skimmer area is clean, filter is clean. I’ve tested CYA again and it’s at 50. All other levels look pretty good. PH is a little high (8.0), but probably expected from this much liquid chlorine. TA is 70. I’m going to do the OCLT tonight. I’ll report back in the morning.

(Until I get this info into my signature, I have a 20,000 gallon pebbletec pool, 60 sq ft DE filter, variable speed pump, Hayward Navigator vacuum.)

 

[kenn_00]

The OCLT showed zero loss with the filter running on low all night. Then today in just 8 hours I lost 8ppm. My pool gets direct sun most of the day. Could this be a UV problem? Could I be losing 8ppm at CYA of 50?

I’ve always kept CYA closer to 70 or 80 in the past. Maybe I need to do that again.

Any thoughts?

 

[proavia]

Was the pool used today? If not, 8ppm loss is excessive. I'm just up the road from you with a CYA of 50 - I lost 2ppm today, no one used the pool and pool is in full sun until 5 pm.

What was the CC reading? Water clarity - can you easily see details of a quarter dropped in the deep end?

 

[Richard320]

I wonder if you're not a victim of the CYA optical illusion. Maybe it's much lower than you think.

Next time you test it, be sure to do it in full sunlight, and hold the tube only at the very top so maximum light enters the view tube. Then look away and look back so the image doesn't get burned in. And then repeat it a bunch of times. Just pour the solution back into the mixing bottle and try again.

 

[Etchase]

Losing 40-50% of your FC on a sunny day is not unusual. If your OCLT is zero, you don’t have algae. Drop it down to 8 and it will probably be 4 the next day.

 

[kenn_00]

No pool use. No CC. Water is perfectly clear - never looked better.

I’ve been keeping up the high chlorine levels and I’m going to bump up my CYA to about 60 and see what happens.

 

[kenn_00]

I’ll try those suggestions for ensuring the accuracy of my CYA readings as well, thanks!

 

[Etchase]

I’m very interested in your usage after you bump up your cya. I live in Hawaii, and we recently had a UV index of 13, cloudless day with the sun directly overhead at my latitude. Chlorine went from 8 to 3.5, with no overnight loss and CYA at 50. My biggest percentage loss I’ve ever noticed. I’m thinking of lowering cya to 30, because I’ve tried higher levels and never seemed to realize a reduction in chlorine usage, but it’s difficult to tell with all the variables. Glad your pool is looking good.

 

[Fast7]

Losing 40-50% of your FC on a sunny day is not unusual. If your OCLT is zero, you don’t have algae. Drop it down to 8 and it will probably be 4 the next day.

That can be true while referring to maintenance level of Chlorine for given CYA, in this case 6-8 FC. However healthy pool should not loose 40-50% from SLAM level in one day.
There is definitely some issue. Maybe error when performing OCLT test? How fresh are reagents?