Trying to figure out chlorine consumption

[jark87]

A couple of weeks ago, after some heavy rain, I had a quick FC drop over a few days. It had dropped from 8 to 3.5 and I had CYA at 80. Lots of debris in the water from the rains and it just looked dull. Went into SLAM mode, which took quite awhile to pass OCLT because we kept getting rain. Finally passed on Wednesday. Pool is crystal clear and I’ve been even more diligent than normal about keeping it brushed and clean. After passing the OCLT (only lost .5 FC overnight), I set the SWCG to 50% and run the pump 14 hours. CYA has dropped to 70 (maybe even 60) because of the rain. I didn’t test Thursday or Friday, but today FC is down 3.5 (from 17 to 13.5). Since I’m running the SWCG, that’s a big drop in only 3 days. According to PoolMath, I should be raising FC by 1.7 based on the pump run time. There’s been no rain since passing the OCLT, but the sun has been bright and hot. Pool has lots of sun exposure. Factoring in the FC that’s supposed to generated by the SWCG, my total FC loss is 8.6 over 3 days. That’s a lot, isn’t it?

Am I looking at this correctly? I’m trying to figure out if I have a salt cell issue. It was just replaced last November, so it’s under warranty.

 

[jark87]

Correction - it was Thursday that I passed OCLT. So that changes the math a bit. Total FC loss of 6.9, but over 2 days instead of 3.

 

[Bperry]

Correction - it was Thursday that I passed OCLT. So that changes the math a bit. Total FC loss of 6.9, but over 2 days instead of 3.

Thats only 3.5 per day, within normal range especially for TX.

 

[jark87]

Thats only 3.5 per day, within normal range especially for TX.

Show me how you get that. FC was 17 on Thursday morning before daylight. Today, at mid-afternoon, it’s at 13.5, so that’s a 3.5 drop. But the SWCG was running and should have added 1.7 per day. Not including today, that’s another 3.4, so a total of 6.9, right? Am I not supposed to include the FC supposedly generated by the SWCG? When my SWCG is running at 50% for 14 hours, I normally hold FC steady all summer long, not drop 1.75 per day.

 

[Bperry]

Show me how you get that. FC was 17 on Thursday morning before daylight. Today, at mid-afternoon, it’s at 13.5, so that’s a 3.5 drop. But the SWCG was running and should have added 1.7 per day. Not including today, that’s another 3.4, so a total of 6.9, right? Am I not supposed to include the FC supposedly generated by the SWCG? When my SWCG is running at 50% for 14 hours, I normally hold FC steady all summer long, not drop 1.75 per day.

I just read what you said about total chlorine loss, not realizing you say chlorine was being added. If you are losing chlorine then something isnt working or isnt powered on long enough. What are you trying to calculate?

 

[jark87]

I just read what you said about total chlorine loss, not realizing you say chlorine was being added. If you are losing chlorine then something isnt working or isnt powered on long enough. What are you trying to calculate?

I’m not really trying to calculate anything. Just using a calculation to see if something is wrong, and it appears that something is. Since I passed the OCLT, I’m thinking the SWCG isn’t working as it should. I ran it at 100% for 24 hours back when I first ran into trouble (a couple of weeks ago) and it did increase my FC, but I don’t recall by how much. I didn’t keep track of it because we were getting so much rain, which skewed the results.

 

[Newdude]

After passing an OCLT, now run an overnight gain test at 100%. Pick an easy target like 8 hours making an even 2 FC.

I am already seeing peak season daily loss on sunny days and some others have seen particularly early high UV demand this year also. I don't know if those of us spiked early, or it's going to keep increasing, but its possible everything is fine and you're seeing it too and the 60 CYA isn't cutting it.

Run the gain test and find out.

 

[jark87]

now run an overnight gain test at 100%

Never even thought of that. Great suggestion!

 

[Newdude]

Never even thought of that

It's hard getting out of your own thoughts and seeing the simplest answer. Ask me how I know.

 

[jark87]

So the mystery may be solved. Tested CYA again, as the last test was on a cloudy day. Today’s test shows CYA at 50, which given a weird situation a few weeks ago, makes sense. I was adding liquid CYA when opening my pool and it had jumped from 50 to 80 with 1 bottle, which should have been impossible because 1 bottle usually increases CYA by 10ish. I tested multiple times over 2 days because I didn’t believe it, but kept getting that result. Well, turns out, I must have done something wrong and today’s CYA test is more realistic. Just added another bottle and will test again in a couple of days and probably add 1 more. That should get me to 70ish and might even push 80. I still plan to conduct the FCGT, just to make sure the SWCG is ok.

Thanks to you both for responding! Love me some TFP!

 

[Newdude]

Many of us figure out the CYA dipped when the FC stops holding. No new news there. Welcome to the club. We meet on the 3rd Wed of each month.

 

[jark87]

Well, turns out it was a salt cell problem, too. Went to Leslie’s to pick up more CYA and for grins had them test the water. I had tested earlier that morning and had FC at 12. Their test showed 6, which I just assumed was off. Well, it really was 6. Ran the cell at 100% overnight and got an increase of 1. Should have been around 3. Contacted my builder who had replaced the cell last year and they had Jandy out this afternoon. I don’t think the guy even tested the cell - he just put a new one in, including sensor, new plug/wiring, etc. Gotta love a warranty replacement with quick service!

 

[jark87]

Well, this is turning into a saga. While the tech was replacing the salt cell, I looked out the window and noticed the spa water level had dropped quite a bit. I went out and asked him about it and he said it was because he had to drain the filter without getting the equipment pad wet. How he did that I don’t know, as I’ve never done it. This morning, I wake up to an empty spa. I contact the tech and after a little back and forth, he says it has to be the check valve and his work had nothing to do with that. I don’t believe in coincidences, but since I had a spare check valve flapper, I just replaced it. Well, that didn’t work - spa still drains when pump is shut off. And I’m getting dirty water flowing back into the filter pump basket when the pump is shut off. The tech was dispatched by Jandy, who was called by my pool builder. He’s washing his hands of the situation and I really don’t want him back. I’ve reached out to my builder to see what they’ll do. Good grief.

 

[jark87]

Simple fix - the tech had turned the actuator for the spa fountain off. Man, from what I thought was a chlorine loss due to heavy rains, to a long (and expensive) SLAM because of continued rain, to a SWCG warranty replacement (the original culprit), to an unnecessary check valve replacement, to a simple actuator switch. Glad all of that’s behind me, especially now that summer is kicking into high gear. Forecast is in the 90s with sun and no rain for the foreseeable future. Pool is crystal clear and ready for action!