Rapid FC loss

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timmer21

timmer21

Active member
Nov 2, 2021
32
Manchaca, TX
Pool Size
7000
Surface
Fiberglass
Chlorine
Salt Water Generator
SWG Type
CircuPool Edge-25
Hope y’all can help me understand why I’m loosing FC so fast. I performed the OCLT last night. FC was at 10ppm at 10 pm. At 7am this morning before the sun hit the pool the FC was 2.5ppm. Not it is 1.5. My chemistry readings are as follows testing with TF100 test kit.
FC 1.5
CC 0
CYA 40
pH 7.5
TA 90
CH 300
Water temp 87
Pool is crystal clear and in direct sunlight from 8 am to 7pm.
I’ve checked and cleaned water feature, skimmer and LEF light niche. I also cleaned my cartridge filter yesterday before doing OCLT. I’m using 7.5% bleach for chlorinating. My pump runs low speed 24/7 and high speed when using water feature or pool sweep.

Any suggestions?
 

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timmer21 said:
FC was at 10ppm at 10 pm. At 7am this morning before the sun hit the pool the FC was 2.5ppm.
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That is an incredible drop in FC overnight and would normally indicate algae somewhere. With no sunlight, organics would be the first assumption unless there is a testing error. Any chance of that? Let's be sure:

10 ML water sample with ONE generous scoop of powder. Mix and add drops until clear then divide answer in half. Example - 24 drops equals an FC of 12. Is that your testing method?
 
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Texas Splash said:
That is an incredible drop in FC overnight and would normally indicate algae somewhere. With no sunlight, organics would be the first assumption unless there is a testing error. Any chance of that? Let's be sure:

10 ML water sample with ONE generous scoop of powder. Mix and add drops until clear then divide answer in half. Example - 24 drops equals an FC of 12. Is that your testing method?
Click to expand...
Yes I retested it twice this morning. I did a SLAM on it 2 weeks ago as I was out of town and the water was a little cloudy when I got back and no FC.
 
Chlorine is consumed by two things only......UV from the sun and organics in your pool. That's a whopping organic loss you got and. like Pat, I wonder whether there is a testing error.

If not, SLAM the pool ASAP!
 
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duraleigh said:
Chlorine is consumed by two things only......UV from the sun and organics in your pool. That's a whopping organic loss you got and. like Pat, I wonder whether there is a testing error.

If not, SLAM the pool ASAP!
Click to expand...
duraleigh said:
Chlorine is consumed by two things only......UV from the sun and organics in your pool. That's a whopping organic loss you got and. like Pat, I wonder whether there is a testing error.

If not, SLAM the pool ASAP!
Click to expand...
I’m following the testing as outlined in the TF 100 kit. I was planning on doing a SLAM but wondered if I was missing something. My pool had been much better since I found this site and got a good test kit last fall.
 
SLAM away! :) I am also puzzled by that really unusual chlorine loss. I hope it's just an anomaly and you get back to losing 2-4 daily like most Texas pools. YYour Slam is almost complete, anyway, with crystal clear water and cc's of less than 1.0 (right?) So all you need is to pass the OCLT and you are in business. Keep us posted
 
timmer21 said:
I’m using regular bleach, concentrated 7.5% available chlorine, from H‑E‑B.
Click to expand...
duraleigh said:
SLAM away! :) I am also puzzled by that really unusual chlorine loss. I hope it's just an anomaly and you get back to losing 2-4 daily like most Texas pools. YYour Slam is almost complete, anyway, with crystal clear water and cc's of less than 1.0 (right?) So all you need is to pass the OCLT and you are in business. Keep us posted
Click to expand...
OCLT last night FC was 16 at 9pm. This morning FC is at 3.5 and CC is 0.5. Water is crystal clear. Continuing the SLAM.
 
For a pool that is crystal clear and negligible cc's, that may be the largest overnight FC loss I can remember! :oops:

Science is inescapable, though, something organic is in your pool and the answer is always the same...........keep high levels of chlorine in there until you oxidize whatever it is. I bet that loss drops of VERY suddenly in the next 24 hours or so.
 
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duraleigh said:
For a pool that is crystal clear and negligible cc's, that may be the largest overnight FC loss I can remember! :oops:

Science is inescapable, though, something organic is in your pool and the answer is always the same...........keep high levels of chlorine in there until you oxidize whatever it is. I bet that loss drops of VERY suddenly in the next 24 hours or so.
Click to expand...
I’m hoping for that result!
 
duraleigh said:
For a pool that is crystal clear and negligible cc's, that may be the largest overnight FC loss I can remember! :oops:

Science is inescapable, though, something organic is in your pool and the answer is always the same...........keep high levels of chlorine in there until you oxidize whatever it is. I bet that loss drops of VERY suddenly in the next 24 hours or so.
Click to expand...
Loss is dropping slower. Your comment about something organic in the pool triggered a thought. I have several potted plants on the wall where my water feature is. When they get watered sometimes the excess water drains out into the pool! Organic material!
 
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When they get watered sometimes the excess water drains out into the pool! Organic material
Click to expand...
Well, some, perhaps but I am not sure that could account for your precipitous loss. Nevertheless, you are slowing down the loss and I think the rest will go smoothly
 
I can see from your logs that fc has dipped below minimum for your cya several times allowing algae to grow. The higher doses of liquid chlorine have kept it at bay but won’t eradicate it. Keep Slammin’ & kill it for real!
After your SLAM Process is complete & u are sure u have passed ALL 3 end of slam criteria you should confirm cya is at a solid 40ppm & aim for the high target fc level for your cya or a scooch above so you don’t broach minimum. This ensures u always have a buffer. Some in your area even find they need a cya of 50ppm in the peak of summer- FC/CYA Levels
 
Thunderstorm last evening dropped 1.9 inches of rain in my pool. FC was 9.0 when the rain started. This morning it is 6.0 I think some of the FC loss is due to dilution from the rain. Pool is still crystal clear and CC is at 0.
 
Mdragger88 said:
I can see from your logs that fc has dipped below minimum for your cya several times allowing algae to grow. The higher doses of liquid chlorine have kept it at bay but won’t eradicate it. Keep Slammin’ & kill it for real!
After your SLAM Process is complete & u are sure u have passed ALL 3 end of slam criteria you should confirm cya is at a solid 40ppm & aim for the high target fc level for your cya or a scooch above so you don’t broach minimum. This ensures u always have a buffer. Some in your area even find they need a cya of 50ppm in the peak of summer- FC/CYA Levels
Click to expand...
Mdragger88 said:
I can see from your logs that fc has dipped below minimum for your cya several times allowing algae to grow. The higher doses of liquid chlorine have kept it at bay but won’t eradicate it. Keep Slammin’ & kill it for real!
After your SLAM Process is complete & u are sure u have passed ALL 3 end of slam criteria you should confirm cya is at a solid 40ppm & aim for the high target fc level for your cya or a scooch above so you don’t broach minimum. This ensures u always have a buffer. Some in your area even find they need a cya of 50ppm in the peak of summer- FC/CYA Levels
Click to expand...
Texas Splash said:
We got hit with some storms yesterday as well. It could just be the fresh rain water on the surface hasn't quite mixed with the pool water. Something to watch though and adjust later if necessary.
Click to expand...
My pump runs 24/7 so is well mixed.
Mdragger88 said:
Carry on until u get a good Overnight Chlorine Loss Test.
You’re almost to the finish line, don’t let off the gas now ! 🏁
P.S.
Your pool is gorgeous 🤩
Click to expand...
Thanks. Just bumped FC up to 15.5. It’s partly cloudy today so not intense sun on the pool. Yet!🤣
 
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