How to “catch” the FC level

[SpockF4]

Just finished my first SLAM and the water looks great! Thank you guys/girls!! Here are the current numbers from Taylor kit:
FC……9ppm
CC….. 0
PH…….7.8
TA…….120
CH……220
CYA….64
My question: The FC has been drifting down from the SLAM level but now how much chlorine do I add to maintain the current level? It’s my first time using liquid chlorine and I’m not sure how much and at what intervals to add for maintenance as opposed to keeping it at SLAM levels. 12000 gal using liquid chlorine now. Appreciate any inputs.
Thanks.

 

[mas985]

As the FC was dropping from the SLAM, do you have daily measurements? This will give you ratio or percentage loss each day which you can then use to up the FC for each day's loss. It should be around 25% lost each day.

Also, at a CYA of 64, I would target something closer to 7 ppm assuming the SLAM was successful.

FC/CYA Levels

 

[Jimrahbe]

F4,

How long did your SLAM last???

Thanks,

Jim R.

 

[ajw22]

A typical pool in your area consumes 3 to 4ppm of FC daily.

Use PoolMath

BTW, there is now way a Taylor test can measure a CYA of 64. Round up to the nearest line. Your CYA is 70.

 

[JJ_Tex]

Is your chlorine 10% strength? If so a gallon will raise your pool's FC by 8.3.

My guess is that you will need 1/4 to 1/2 gallons per day for maintenance, but that is where testing is needed to make sure you have a good handle on it.
Speaking of testing, how are you testing?

 

[summertimesadness]

As the FC was dropping from the SLAM, do you have daily measurements? This will give you ratio or percentage loss each day which you can then use to up the FC for each day's loss. It should be around 25% lost each day.

Also, at a CYA of 64, I would target something closer to 7 ppm assuming the SLAM was successful.

FC/CYA Levels

Curious as I am doing the same thing in the OP.

25% of the number that was in the AM should be approximately what it was starting at sun down? Obviously the higher the FC, the larger the # for the 25% reduction.

 

[mas985]

25% of the number that was in the AM should be approximately what it was starting at sun down? Obviously the higher the FC, the larger the # for the 25% reduction.

The LOSS is 25%. Ratio of night to morning is 75% under a 25% loss scenario.

25% ~ 1 - FC Night / FC Morn

But 25% is a rough estimate.

 

[summertimesadness]

The LOSS is 25%. Ratio of night to morning is 75% under a 25% loss scenario.

25% ~ 1 - FC Night / FC Morn

But 25% is a rough estimate.

Maybe I'm missing understanding.

If my FC is 25 at 8am (let's say that's when the sun starts on the pool), during my SLAM period, then after the sun goes down, provided the CHL wasn't being chewed up by anything but the sun, it would be 25% of 25 that should be reduced, correct? (Or 6.25)

Then next 8am test would be approximately, give or take, 18.75. If no algae is eating at the CHL over night, should be within 1ppm of that.

Then that new number would be reduced by approximately 25% throughout the day?

If the higher the FC the more it gets chewed through is true.

 

[mas985]

Yes, that is correct. UV extinction is a percentage loss of current FC levels and is dependent on CYA level as well as sun angle and cloud cover.

 

[summertimesadness]

Yes, that is correct. UV extinction is a percentage loss of current FC levels and is dependent on CYA level as well as sun angle and cloud cover.

Thank you.

 

[SpockF4]

SLAM TOOK ABOUT 2 weeks. Thanks for all the input.

 

[SpockF4]

Also I did the CYA test using the half tap water method and doubling the result read on the scale. I guess I should round up regardless?

 

[Jimrahbe]

SLAM TOOK ABOUT 2 weeks. Thanks for all the input.

F4,

I want to apologize for what I was thinking..

I have no idea why, but for some reason I got the impression that you SLAMed the pool in one day, which of course would not be much of a successful SLAM.

Glad to hear I was wrong...

Thanks,

Jim R.

 

[Mdragger88]

Also I did the CYA test using the half tap water method and doubling the result read on the scale. I guess I should round up regardless?

Yes - better safe than sorry. Aim for high target
FC/CYA Levels
then replenish fc before you get near minimum- minimum is lava
The chart & targets are set up that by doing this (aiming for high target) & testing daily you should have no issue keeping away from minimum.

 

[MITBeta]

Also I did the CYA test using the half tap water method and doubling the result read on the scale. I guess I should round up regardless?

Does that mean that you measured 32 and doubled it to get 64? Or that you diluted by half and measured 64, which means your CYA is really 130?