1st pool, new to the TFPC method! Question on FC use during the day.

jeffboer

Member
Jun 3, 2019
15
Indiana, USA
Hello! I’m the proud new owner of a 30,000 gallon in-ground vinyl liner pool! We purchased the house towards the end of the season last year, and followed the previous owner’s advice on closing at the end of last season and opening at the beginning of this season- he was a diehard Leslie’s fan! After just a few weeks I was already sick of trips to the pool store, and a botched water test at Leslie’s sent me to Google looking for a better way...and here I am! Current test results:
FC: 3
pH: 7.5
TA: 110
CH: 170
CYA: 50

I bumped FC to 8 yesterday evening, and was still at 8 this morning, but was down to 3 by this evening. Wondering if this is normal FC loss during the day. It was a sunny day, in the Mid 70s, and pool has a lot of direct sunlight during the day.

FC range based on CYA is 4-8...if 5ppm loss is expected during the day, should I bump up to 9 or 10 in the evening so I stay above the minimum 4ppm?

Thanks so much I’m advance for the advice!
 

Richard320

TFP Expert
LifeTime Supporter
Jan 6, 2010
22,054
San Dimas, CA (LA County)
Welcome! :wave:

I question whether that 50 CYA is accurate or not. You should only be losing 2 or 3 FC under the conditions you describe unless there were a lot of swimmers. Or even one swimmer with a weak bladder :rolleyes:

That test is the hardest to master. It has to be done in bright sunlight. Indoor lighting isn't enough. If it's dark, the dot is harder to see and it disappears sooner, reading falsely high. Try it again in full sunlight, only holding the viewtube at the very top.
 

trivetman

Bronze Supporter
Jul 14, 2017
217
Jenkintown, PA
Hi Jeff - 5 seems like a lot but I think every pool is different. You can expect a loss of at least 2 or 3 on a hot sunny day. If its cold and cloudy I’ll lose less than 1.

You didn’t lose any FC overnight so thats a good sign your water is in good shape.

If you end up losing 5 daily on a regular basis then I would bump up to 9-10 at night like you said so you stay above 4. The other option would be to add FC twice daily. Maybe mid-morning and then the evening. You might go through less that way as you’re having to bump it up so high. The higher the FC level the faster you lose it
 

jeffboer

Member
Jun 3, 2019
15
Indiana, USA
Welcome! :wave:

I question whether that 50 CYA is accurate or not. You should only be losing 2 or 3 FC under the conditions you describe unless there were a lot of swimmers. Or even one swimmer with a weak bladder :rolleyes:

That test is the hardest to master. It has to be done in bright sunlight. Indoor lighting isn't enough. If it's dark, the dot is harder to see and it disappears sooner, reading falsely high. Try it again in full sunlight, only holding the viewtube at the very top.
Thanks for the response! Only had a few swimmers today for about 30 minutes since it was rather chilly! Are you thinking CYA may be lower than 50, resulting in the excess chlorine not bound to CYA burning off quickly? I am new at the testing, I’ll need to retest CYA in the method you describe to verify numbers. Maybe I should take to Leslie’s? 😁
 

mknauss

Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
20,592
Laughlin, NV
When you do the CYA test, try this next time.

Once you have your solution ready, back to the sun, etc. Fill the vial to a line, say 80, lower the vial to your waist level and glance for the dot, you see it, add solution to the 70 line, glance, see it, repeat until you no longer see it with a glance. Then use the CYA value one step above the line you read. So if you stopped at 50, use 60 ppm CYA.

The vial is in logarithmic scale. So it is not viable to interpolate between the lines. Just use the whole numbers, such as 50, 40, 30, ....
 
  • Like
Reactions: jeffboer

jeffboer

Member
Jun 3, 2019
15
Indiana, USA
When you do the CYA test, try this next time.

Once you have your solution ready, back to the sun, etc. Fill the vial to a line, say 80, lower the vial to your waist level and glance for the dot, you see it, add solution to the 70 line, glance, see it, repeat until you no longer see it with a glance. Then use the CYA value one step above the line you read. So if you stopped at 50, use 60 ppm CYA.

The vial is in logarithmic scale. So it is not viable to interpolate between the lines. Just use the whole numbers, such as 50, 40, 30, ....
Thank you, will update with the results!
 

Richard320

TFP Expert
LifeTime Supporter
Jan 6, 2010
22,054
San Dimas, CA (LA County)
Thanks for the response! Only had a few swimmers today for about 30 minutes since it was rather chilly! Are you thinking CYA may be lower than 50, resulting in the excess chlorine not bound to CYA burning off quickly? I am new at the testing, I’ll need to retest CYA in the method you describe to verify numbers. Maybe I should take to Leslie’s? 😁
:mrgreen:
 

jeffboer

Member
Jun 3, 2019
15
Indiana, USA
Retested CYA this afternoon in the method described, got 40 this time, as opposed to the 50 I got in my earlier testing. FC was at 9 this morning, down to 4 this evening. Bumped to 7 tonight (the top of the FC range based on CYA), will see what loss is during the day tomorrow!