I'd like to point out that one major difference between your pool water and the bleach sample is the bleach has no CC and your pool clearly does. Perhaps the slow return of pink during the pool water test is some of the CC becoming FC without the reagent you add before the CC test. If this is the case, your CC is realy quite higher than you are presently measuring. I've read many if not all of your posts (and I'm not going to re-read them) and I don't think you've actually gotten your FC to shock level and held it there (if this is wrong, I'm sorry). This could be exacerbating the situation. You keep adding chlorine and producing CC but you never get the level high enough to clear up the CC.

You could test this with a bucket of pool water say about 4 gallons. Add 1/2tsp of your self certified 12.5%. Should bring your FC up about 20ppm. Stir. Measure FC and CC stopping the FC test the first time it goes to clear.