Sudden drop in FC

[TeenaTeens]

Yesterday I put a bag of salt and 68 oz of muriatic acid in the pool. Had to drop the TA. Also had the salt cell replaced early afternoon yesterday. FC dropped overnight to 1! I just checked the water coming out of the return - it tested at 3 so the salt cell is producing. I’ve dropped some liquid chlorine in, but have to do a Leslie’s run st 9am and am superchlroninating right now.

CC tested clear. Any idea what could have caused the FC to drop so drastically? Only two swimmers yesterday, nothing out of ordinary, I test FC daily with Water Guru and a few times a week with my kit. It was normal yesterday when I Taylor’s tested before adding the salt and acid and new cell.

 

[Texas Splash]

So your FC went from 8 to just 1 in about 18 hours? If there were no testing errors, I think an Overnight Chlorine Loss Test is in order. Do that first before tinkering with anything else.

 

[TeenaTeens]

So your FC went from 8 to just 1 in about 18 hours? If there were no testing errors, I think an Overnight Chlorine Loss Test is in order. Do that first before tinkering with anything else.

So weird right? I’ll boost it today as I have people coming over and do the OCLT tonight. Water is clear. And no testing errors - water guru and Taylor’s match exactly.

 

[TeenaTeens]

So weird right? I’ll boost it today as I have people coming over and do the OCLT tonight. Water is clear. And no testing errors - water guru and Taylor’s match exactly.

The acid and salt wouldn’t have caused it to drop would it? My balancing has been spot on since I slammed last year. Only change has been those flakes last week and lowing my TA. Usually I do that in two goes - drop the Ph to 7.4 twice, busy yesterday I decided to do it in one go. Maybe that wasn’t wise.

 

[Texas Splash]

The acid and salt wouldn’t have caused it to drop would it?

No, no relation. Good you caught it when you did. Hopefully it holds better today and this evening for your OCLT. Have a great day.

 

[Mdragger88]

Use liquid chlorine to get in target range ASAP- do not wait on “super chlorinate” it is too slow. It only means that it runs at 100% for 24 hours or until the pump turns off (& then you need to remember to turn the swg back on). It doesn’t mean it puts out more chlorine now.
The max fc that cell (t5) can produce in your pool in 24hrs is around 7ppm.

A t9 cell or larger would be more ideal for your pool in sunny florida with long summers.
After you pass an
Overnight Chlorine Loss Test at target fc levels ruling out algae you can do an overnight chlorine gain test to see if the cell is doing what it should.

 

[JamesW]

Calcium chloride and sodium chloride can sometimes (Maybe) cause a loss of FC that we cannot explain.

There is no chemical reason adding calcium chloride or sodium chloride would cause a loss of FC, but anecdotal reports indicate that it might happen.

Possibly some sort of contaminant in the products.

 

[TeenaTeens]

Use liquid chlorine to get in target range ASAP- do not wait on “super chlorinate” it is too slow. It only means that it runs at 100% for 24 hours or until the pump turns off (& then you need to remember to turn the swg back on). It doesn’t mean it puts out more chlorine now.
The max fc that cell (t5) can produce in your pool in 24hrs is around 7ppm.
View attachment 510330
A t9 cell or larger would be more ideal for your pool in sunny florida with long summers.
After you pass an
Overnight Chlorine Loss Test at target fc levels ruling out algae you can do an overnight chlorine gain test to see if the cell is doing what it should.

I added liquid chlorine immediately. Tested again and I’m about to test again to see if I need to add more before the OCLT I’m doing tonight. So you think changing to a t-9 cell would be better than the t-15? I have a new one in, and a new spare one, so don’t really want to replace it until needed. But maybe I’ll sell them and buy a bigger one…

 

[TeenaTeens]

Use liquid chlorine to get in target range ASAP- do not wait on “super chlorinate” it is too slow. It only means that it runs at 100% for 24 hours or until the pump turns off (& then you need to remember to turn the swg back on). It doesn’t mean it puts out more chlorine now.
The max fc that cell (t5) can produce in your pool in 24hrs is around 7ppm.
View attachment 510330
A t9 cell or larger would be more ideal for your pool in sunny florida with long summers.
After you pass an
Overnight Chlorine Loss Test at target fc levels ruling out algae you can do an overnight chlorine gain test to see if the cell is doing what it should.

I thought t-9 produces less than t-15…

 

[TeenaTeens]

Calcium chloride and sodium chloride can sometimes (Maybe) cause a loss of FC that we cannot explain.

There is no chemical reason adding calcium chloride or sodium chloride would cause a loss of FC, but anecdotal reports indicate that it might happen.

Possibly some sort of contaminant in the products.

So it could have been the salt? The pool has maintained the FC today despite four people spending hours in it. I upped it with liquid chlorine this morning as soon as I saw the test results, ran the SWG at 60% which is my normal range to keep it at around 7 which is where I keep it. I’ll wait until dark now and rest it again. And again before the sun comes up. Just the strangest thing - absolutely no reason I can see that it would have dropped except either the salt or the acid which seems very unlikely. I test FC every day - there hasn’t been a drop in a year since I did my last slam. I have been testing more often over the past week or so as I upgraded to the water guru 2 and have been comparing for accuracy. Very strange indeed. I also cleaned the filter today even tho I only did it a couple of weeks ago - it was extremely clean.

 

[JamesW]

Sometimes anomalies happen that we cannot explain.

 

[TeenaTeens]

Sometimes anomalies happen that we cannot explain.

Well I hope this is one of those - we shall see what the OCLT shows us.

 

[TeenaTeens]

Use liquid chlorine to get in target range ASAP- do not wait on “super chlorinate” it is too slow. It only means that it runs at 100% for 24 hours or until the pump turns off (& then you need to remember to turn the swg back on). It doesn’t mean it puts out more chlorine now.
The max fc that cell (t5) can produce in your pool in 24hrs is around 7ppm.
View attachment 510330
A t9 cell or larger would be more ideal for your pool in sunny florida with long summers.
After you pass an
Overnight Chlorine Loss Test at target fc levels ruling out algae you can do an overnight chlorine gain test to see if the cell is doing what it should.

I have a t-15 not a t-5

 

[TeenaTeens]

I thought t-9 produces less than t-15…

It does - it produces 14 on superchlorinate over 24 hours. I had it incorrectly labeled in my profile - I fixed it.

 

[Mdragger88]

I have a t-15 not a t-5

That’s even better! Fantastic

 

[TeenaTeens]

So it could have been the salt? The pool has maintained the FC today despite four people spending hours in it. I upped it with liquid chlorine this morning as soon as I saw the test results, ran the SWG at 60% which is my normal range to keep it at around 7 which is where I keep it. I’ll wait until dark now and rest it again. And again before the sun comes up. Just the strangest thing - absolutely no reason I can see that it would have dropped except either the salt or the acid which seems very unlikely. I test FC every day - there hasn’t been a drop in a year since I did my last slam. I have been testing more often over the past week or so as I upgraded to the water guru 2 and have been comparing for accuracy. Very strange indeed. I also cleaned the filter today even tho I only did it a couple of weeks ago - it was extremely clean.

Update - OCLT passed with flying colors. I tested twice with both Taylor’s and WaterGuru and got exactly the same results. I am stumped - the dip was not a false reading. It was also tested multiple times with both methods. I’m not sure what to do apart from just keep doing what I’m doing…

 

[Texas Splash]

Update - OCLT passed with flying colors.

That's great. As James noted above, it appears you may have experienced one of those very odd situations that seems to have no definitive explanation. But you're on top of things with your testing, so continue the great work.

 

[TeenaTeens]

That's great. As James noted above, it appears you may have experienced one of those very odd situations that seems to have no definitive explanation. But you're on top of things with your testing, so continue the great work.

All because of the amazing help I’ve received here over the past year. Fingers crossed it’s an anomaly and it’s back to business as usual. Thank you.

 

[Mdragger88]

Whatever it was, its gone now!
Hooray
Thank goodness for your adamant testing or you may not have known there was anything wrong until it looked funky. Good job

 

[TeenaTeens]

Whatever it was, its gone now!
Hooray
Thank goodness for your adamant testing or you may not have known there was anything wrong until it looked funky. Good job

It’s why I love the water guru. Every morning I get a result - if it’s wonky, I test straight away. I just upgraded to the sense 2 and it’s pretty accurate - far more that the 1 which I had for a year. Doesn’t replace my Taylor’s bi weekly testing - but it sure helps me avoid things like this. It literally made it keep yesterday!!! Or else I wouldn’t have tested until today or tomorrow and it would have been too late and slam time. I just wish I knew what caused it. Will do another OCLT later this week to be sure. And will test again throughout the day to make sure it’s holding onto the chlorine. So very odd.