Possible undersized SWG

[Chad's Pool]

Good morning,
I am having a hard time maintaining my free chlorine levels. This will be the third year with this setup and I haven't had an issue until now. My pool is approximately 15000 gallon fiberglass and the builder installed a Hayward T3 cell.

Current tests: Using TF100 kit
C = 6.5
CC = 0.5
PH = 7.6
Alka = 90
Cal = 300
CYA = 60-70
Salt = 3300

I slammed the pool last week and have allowed the free chlorine to drift down. I performed an overnight chlorine test last night and passed (dropped 0.5ppm) My recent free chlorine readings are as follows:
Thursday = 11.0 SWG at 85%
Friday = 10.5 SWG at 85%
Saturday = 7.0 SWG at 90%

The cell is clean and the voltage and amperage are within their normal operating limits. I'm wondering if the cell is just too small to keep up with the chlorine loss, but also wonder if that is the case, why didnt I have problems last year?

Thank you for your help,
Chad

 

[mknauss]

A T3 cell should be able to add 4 ppm FC to your pool in 24 hours at 100%. So on the edge but should keep up most of the time.
Check your CYA -- I find a big change from 60 to 70+ CYA. FC loss slows at the higher CYA.

You will see daily variations of FC. The key is to keep it well above minimum. Which it appears you are.

Please add what test kit you are using to your signature.

 

[Chad's Pool]

Thank you,

I actually run the system 12 hours per day not 24 Which was able to keep up last year. I may have to weigh my Cost options of running it 24/7 or replacing the cell with a t-9. Do you have any idea how much higher the free chlorine should be coming directly out of the return. I tested that in an effort to make sure the cell was generating chlorine and it was 8 ppm which is 1.5 ppm higher than the pool.

thanks again
Chad

 

[mknauss]

The FC coming out of the cell is just marginally higher than the pool. I am surprised you saw that much of an increase.

Running at 12 hours per day is not sufficient. Last year may have been different weather conditions, etc but that would be 2 ppm of FC per day and that is the absolute lowest a normal pool will use, unless covered or heavily shaded from the sun.