I have a few year old, vinyl, in ground, SWG fed pool. It has been super easy going for the most part and I've been an avid follower/learner of the TFP. I even use my TF-100 kit as my go to indicator of health for my pool. Until this year when I got lazy...
Upon opening the pool, it had started going green. Because I was at Lowe's already and didn't feel like driving for Clorox, I just bought a box of the powdered, dichlor Shock. Worked just fine on the green and had crystal clear water in no time. Over the next few weeks, I started noticing that annoying "dust" building up overnight. My chlorine levels were fine. No overnight loss... no CCs. Odd. Then it went from a mild annoying "dust" to ... uh oh, we've gone cloudy. It didn't make sense. My chlorine was fine!! So I thought. Then I sat down and checked my CYA to find that it had jumped to about 100. Oh... Thanks, dichlor!!
I went back to Pool School and did some reading again, especially Chem Geek's wonderful posts on Pool Water Chemistry that led me to knowledge... that my running, target FC of 5, while totally sufficient at my previous 70 CYA levels, was totally INSUFFICIENT at a CYA of 100. Off to the store, this time, for regular old, 5.7% BLEACH! After boosting to SLAM levels, proper monitoring, and return to swimming levels, I am pleased to say that not only is my pool water crystal clear again, but more importantly, I have learned my lesson. No more dichlor. No more guesswork when things start going "odd". No more using HALF of the TFP method and half of whatever is right in front of me at the time.
I see all the posts of people going through this same journey. (Ok, I'll SLAM, but still use my old pool store chlorine supply.) It is hard to let go sometimes and just trust something so simple, but the TFP method not only works, but the knowledge inside of it saves you from chasing your tail in an endless struggle while you treat one problem while causing 2 more. So even though you weren't directly involved in this exercise, thanks to everyone who helped put all this knowledge out there. Especially Chem Geek!