You don't necessarily need to backwash unless your filter pressure is 6-8 psi over your "clean" pressure. In fact, the dirtier sand often filters better than clean sand. However, if you're seeing a lot of pressure increase, then by all means backwash it. You might consider using skimmer socks, which can be found at most pool stores. It's just a fine mesh "sock" that fits inside the skimmer basket, like a coffee pot liner. You'd be amazed at how much stuff they catch that you don't even realize is in the water.

I wouldn't be concerned that the CC keeps reappearing....the CC indicates that the chlorine is working on something, and that's why we have it in there. People swimming in the pool introduce sweat, sunscreen, and other stuff we don't have to mention here and your trees are introducing pollen and other stuff. So it's not unexpected to see CC appear and disappear--but you don't want them over 1.0. If it goes over 1.0, then it's time to shock the pool.

I am more concerned about the 2 ppm chlorine loss overnight--usually the rule of thumb is that if you lose less than 1 ppm overnight, then you can let the chlorine drift back down--but since yours is 2 ppm, AND you have residual CC, I'd let it stay at shock level another night and see what it looks like tomorrow.

Does brushing that green ring make any difference?

Janet