New t-cell not maintaining FC levels

[OrangeAndBlue]

Hi SWG experts,
The original t-cell that was installed by the pool builder finally died earlier this month after about 5 1/2 years of service. I ordered a new Hayward OEM T-15 cell and installed it about 2 weeks ago. This new cell just doesn't seem to produce as much FC as my previous one. Has anyone had any similar experience before or have ideas for what else I could try?

Here is where I stand and what I've done so far:

• In the peak of summer like we are in right now, the old cell would maintain steady FC running at 80% for about 8-10 hours per day. Now I'm running 12 hours a day at 100% and I'm still losing 1ppm of FC every 3-4 days.
• It has been a particularly hot July here in Texas, but we've dealt with a week of 100+F before with this pool and I don't recall increasing FC demand this significantly.
• I've done a OCLT last week and passed: Measured FC of 6 at sunset. Tested 2x at sunrise just to be sure and measured 5.5 and 6 FC.
• Tested salt level is 3400. Aquarite panel displays 3300. There are no faults in the panel. I've done the salt level calibration a few times and the instant salt reading consistently settles at 3300.
• Confirmed the Aquarite panel is set to t-15.
• Visual inspection of the cell and plates doesn't show anything obviously suspicious.
• FC in the pool has never dropped below 4 since my old cell started dying on me earlier this summer.

Full test results from yesterday:
FC: 4.5 (I have added ~30oz of bleach since this test)
pH: 7.6
TA: 70
CH: 475
CYA: 50 (I'm adding 2 lbs via a sock in the pool right now)
Salt: 3390 (I'm only using AquaCheck test strip for salt, but this measurement has been consistent with every test in the past month)
Temp: 90-93 F most of the time for the past 2-3 weeks. Pool gets full sun most of the day.

The old cell was a Hayward T-15, and I've replaced it with a Hayward OEM T-15 cell, unless I've been duped. I got it online from Target (they sell it online, believe it or not, but from a 3rd party seller). I bought it there because I could get 5% off and hopefully easy 90 day returns. I've registered it with Hayward for the warranty, but at this point I'm debating just taking it back to Target and buying another one from a local pool store.

 

[mknauss]

Likely low CYA and high UV. Wait for the CYA to be at or above 70 ppm and see how the generation shows. It may not be exactly the same as the last cell, there are variations.

 

[OrangeAndBlue]

Thanks, let's hope so. I will keep tracking it now that I have added CYA. The forecast continues to be very hot and sunny, just as it has been, so we will see if adding CYA improves anything while the weather stays constant. I will report back.

I'm still a bit baffled by the huge difference. If my SWG was running 10 hrs at 80% (equivalent to 8 hours at a 100%) in past summers, and now I need 12 hours at a 100% for similar output, that is a 50% increase in required pump run-time!

I know there are others here in the Houston area with a SWG. Have you had to increase your SWG output or run-time noticeably more than normal this past month or so?

 

[OrangeAndBlue]

Thanks @mknauss. Raising CYA seems to have done the trick and it's now more in line with expectations.

Just want to share the difference adding some CYA has made here for anyone else's benefit as well. This has really highlighted the difference proper CYA levels can have to me:

• Before: CYA = 50: 12 hour daily pump run time with SWG set to 100%. Loss of 1ppm FC every every 3-4 days.
• Now: CYA = 80: 11 hour daily pump run time with SWG set to 100%. Gain of 1ppm FC after 4 days.
• Weather has been consistent. Low 100s and sunny every day all day, before and now.

Just bringing the CYA level up into proper range should let me set the pump run time another 1-2 hours hours lower now, and save $$$ both in electric bills and extending the life of the t-cell.