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I was just curious to f you were ever able to get out of the cycle and restore FC levels. Sound like not so much....
terrible product after effects with no end in sight. I’d drain it and start fresh if only I weren’t worried about my inground fiberglass pool getting damaged in the process
It's getting there (CC continues to drop), but I started the treatment 10 months ago! I used 20 lbs of sulfamic acid / #2 in a 17,500 gal. pool instead of the recommended 17.5 lbs so my dosage was a little high, but not that much higher than recommended so I don't think that's my problem.
My guess is that cold water and cloudy weather slows the breakdown of the sulfamic acid-bound chlorine. We've had very little warm and sunny weather this year in N. Idaho and I observed that the CC readings didn't change significantly between closing and opening either. (There's thick ice over the pool for much of the winter here.) In fact, I'd guess that the only CC reduction upon opening that I measured was due to dilution after returning the water level to normal. (I drain down something close to 10% of the pool's volume for closing.)
Now the sun is back out again and CC was dropping last I checked so maybe it takes sun, warmth, AND free chlorine to break down the Jack's #2 chlorine lock. Last I checked (as best as I could check with the timing-dependent FAS-DPD test for sulfamic acid bound chlorine), my FC and CC were about equal. Now that I have at least decent FC showing, I'm just going by the FC results of FAS-DPD testing, which is not dependent on timing--at least not significantly. I usually don't even bother to add DPD test reagent R-0003 to check for CC now. Hopefully the diagnostic value of that part of the test will eventually return completely. I'm guessing around closing time (one full year after treatment began)! In the early stages of the chlorine lock, I recommend the OTO test over FAS-DPD (even if you have to dilute the OTO sample to get "on scale") but no test works very well during the early post-treatment stages, due to the abnormally high timing sensitivity of all tests.
I installed an SWG this year and my CYA is 70. I'm using the TFP calculator's SWG recommendation of 5 ppm FC target as my MININUM. The TFP non-SWG target recommended range is 8-10 ppm FC, so 10 ppm is the maximum I've adopted--at least until my false CC FAS-DPD numbers go away. I've had two algae outbreaks this year, which I've never had previously, but using 5 ppm to 10 ppm FC on the FAS-DPD test and the SWG seems to be working for me now. If you still have very low FC readings, I recommend keeping your TC a bit higher than your normal FC levels until FC returns to something closer to normal. My guess is roughly halfway between normal max target and SLAM should work. Of course mileage always varies between pools!