Big FC drop during the day... but passing OCLT

caliking

Well-known member
May 12, 2012
45
0
Houston, TX
#1
Recent convert to the BBB method. Testing with TF-100, and my numbers are in line with the recommended values for CC, CYA, pH, TA. 18000 gallon, in ground, gunnite pool. Was using trichlor until I noticed brown stains and found my CYA= 100+.

Current values:
FC= 1
CC= 0-0.5
pH= 7.2 (lowered with MA since I am going to work on the stains which could be iron vs Ca scaling)
TA= 110
CYA= 35

So here is my issue- shocked with 6%chlorine up to 13 based on the Cl/CYA chart. Next morning FC fell to 12. At the end of that day the FC had fallen to 7 - sunny day here in Houston, 3 people swam for 1 hr. The following morning the FC was 6. No swimming that day (Memorial Day), now at night the FC is 0.5-1. Added 6% bleach with a target of 10 (to give me some leeway for tomorrow).

I don't think I have any organics/algae since I passed the OCLT. Water is very clear. I thought the daily drop in FC was supposed to be 2-3 not 5-6. Just want to make sure that I'm not missing something.

Thanks!
 

linen

LifeTime Supporter
TFP Expert
Jul 30, 2010
8,649
0
48
Twin Cities, MN
#2
Let me see if I have this correctly, you experienced a drop of 6 to 1 ppm during one day? No signs of CC?

That is a little high, though each pool situation is different. How much sun does your pool get? How hot has it been?

You may want to repeat the OCLT just to be sure.

If the OCLT passes again, you might want to raise the CYA level to 50 ppm to protect your chlorine from the sun a little better.
 

caliking

Well-known member
May 12, 2012
45
0
Houston, TX
#3
The pool gets 10hours of full sun daily, if not more. Temps have been in the low 90's here. Passed the OCLT Sat and Sun nights. Noticed the FC drops on Sun and Mon. Sat night the CC was zero, Sun night the solution turned just a mere blush of pink, but I added a drop of reagent to clear it up, so I counted it as CC=0.5. I will try and bump the CYA up, and hope that helps to stabilize the chlorine.

To be on the safe side, should I add some polyquat60 algaecide? I need the FC to be near zero to address the stains but I'm nervous about the large daily drops in FC, since I won't be able to work on the stains for a week or two.
 

duraleigh

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Mod Squad
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Apr 1, 2007
31,266
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Sebring, Florida
tftestkits.net
#4
I always go back to our old mantra....

There's ONLY two things that consume chlorine, sunlight and organics. If you pass the OCLT and perform it correctly, you have no organics in the pool.
 

march2012

LifeTime Supporter
Jan 21, 2012
369
0
#5
caliking said:
Recent convert to the BBB method. Testing with TF-100, and my numbers are in line with the recommended values for CC, CYA, pH, TA. 18000 gallon, in ground, gunnite pool. Was using trichlor until I noticed brown stains and found my CYA= 100+.

Current values:
FC= 1
CC= 0-0.5
pH= 7.2 (lowered with MA since I am going to work on the stains which could be iron vs Ca scaling)
TA= 110
CYA= 35

So here is my issue- shocked with 6%chlorine up to 13 based on the Cl/CYA chart. Next morning FC fell to 12. At the end of that day the FC had fallen to 7 - sunny day here in Houston, 3 people swam for 1 hr. The following morning the FC was 6. No swimming that day (Memorial Day), now at night the FC is 0.5-1. Added 6% bleach with a target of 10 (to give me some leeway for tomorrow).

I don't think I have any organics/algae since I passed the OCLT. Water is very clear. I thought the daily drop in FC was supposed to be 2-3 not 5-6. Just want to make sure that I'm not missing something.

Thanks!
about 3 weeks ago I was losing 3-4 ppm per day from my pool in austin with a CYA around 30. I bumped it to 45-50 and now lose about 1-2ppm. I think you need more CYA. You will need to keep your FC at around 5.
 

caliking

Well-known member
May 12, 2012
45
0
Houston, TX
#7
Thanks for the info everyone. I won't tell my wife that the CYA is too low now because she wasn't happy when I drained the pool for the second time recently to lower the CYA!