Confusing Pool Series of Events

mikesnead

Well-known member
Jun 15, 2017
58
Winter Park, FL
Greetings all,

My salt water pool has been acting about odd lately. The last few weeks I seem to be losing CYA at a rather rapid rate; for example I went from 70 to 20 between Sept. 1st and today (Sept. 15th). Additionally, my cell seems to have trouble keeping up. Previous months keeping the cell at about 20-30% running 24/7 (low-low speed on a variable speed pump) would keep my FC level in a good range (4-10 depending on loading and sun exposure). Lately I've had it running 100% 24/7 and it can hardly keep 2 to 3 FC and I am supplementing with 10% bleach often.

Most confusing was this morning. Test at 10am before the pool comes out of shadow gave 3.5 FC (0 CC) after the cell had been running 100% for several days straight. CYA had dropped to the 20 I mentioned above so I added 77oz of CYA, 40lbs of salt (cell turned off just prior to addition) and 1.5 gallons 10% bleach (to bring the FC up high while the cell is off for salt to dissolve). I just tested the FC/CC levels and have a reading of ZERO FC and CC. Full latest results below:

10am 9/15/18 test:
FC 3.5
CC 0.0
pH 7.5
TA 60
CA 450
CYA 20
Salt 3400
Temp 87F

~11:30 am added 79 oz dry CYA, 40lbs Salt, 1.5 gallon 10% bleach (Cell turned off from 100%).

2pm 9/15/18
FC 0.0
CC 0.0
pH 7.0 (Expected drop from CYA addition)

OCLT planned for night, if I can get the pool to hold any chlorine. Willy be dumping another gallon shortly.

Anyone have ideas for where my chlorine went? Or where my CYA has been going? We've had pretty normal rains nearly every day. Pool is 100% clean (can see the screw heads on the main drains) and I can see the bubbles pouring out of the returns from the cell running.

Thanks to all who read and/or answer!! I've had zero trouble with this pool up until now :)
 

mikesnead

Well-known member
Jun 15, 2017
58
Winter Park, FL
Added another gallon of 10% bleach. Pump running at max to mix, plus I brushed for about 15 mins. Testing after that gave:

FC 4.5
CC 0.5

Going to add another gallon now.
 

mikesnead

Well-known member
Jun 15, 2017
58
Winter Park, FL
I can't see any more salt on the bottom, so I will turn the cell back on and repost the diagnostics for you.

After adding the additional gallon, I'm up to 10FC, 0.5CC. I'm down to my last gallon :) I'll have to get more tonight.
 

ping

TFP Expert
LifeTime Supporter
Jun 24, 2011
3,018
Long Beach, CA
The cell is producing chlorine with those numbers.

It seems the FC level is not rising as high as it should, with each gallon of chlorine added it should have raised it by 11ppm. Either the chlorine is weak or there is nascent algae consuming the chlorine.

Run the OCLT tonight. Try to get the FC to 10ppm at night and run the pump overnight. Make sure to turn off the SWG before you start the OCLT.
 

mikesnead

Well-known member
Jun 15, 2017
58
Winter Park, FL
The cell is producing chlorine with those numbers.

It seems the FC level is not rising as high as it should, with each gallon of chlorine added it should have raised it by 11ppm. Either the chlorine is weak or there is nascent algae consuming the chlorine.

Run the OCLT tonight. Try to get the FC to 10ppm at night and run the pump overnight. Make sure to turn off the SWG before you start the OCLT.
Will do. I've got my alarms set to remind me to shut down the cell just before sunset and to take the starting measurement just after full dark. My last gallon got my FC up to 17 (from 8.5).

The last three gallons were just purchased today and those prior were only a few weeks old... I should have checked the date codes :mad:

Thanks greatly for all those that have read and/or replied :)
 

mikesnead

Well-known member
Jun 15, 2017
58
Winter Park, FL
Found the date code for the last three jugs. 18 113 which is sometime in April of this year if I figured it right. It came from Home Depot where its stored outside (in shade), so I could see where it might have gone down by as much as 1/2 strength. Once it gets to my house, I store it in an air conditioned store room. (~80F max). The jump in FC from the last jug seems to indicate it was at least near full strength though.

Has anyone heard of or know why CYA would go down by 50 in just two weeks with only normal FL rainfall amounts?