There is no ionizer and no copper algaecide. There was a nature2 in the filter 9 years ago when I bought it, but it was not installed when I started up the pool, and it was a new filter cartridge (so no residue there). The Culator bag is intact and quite firm. I have tried to squeeze it to drain some of the fluid, but it's like a rigid balloon, and I don't want to pop it.
I'd be shocked that there could be enough copper residue from the the original installation (which was dismantled and drained) to have the effect that was observed.
The reason I bought the Culator is because there was 1ppm of iron (according to Leslie's, and I have no independent way to confirm or deny this), so I wanted the iron removed, which it was when I went back to Leslie's for the second time, for what it's worth. Since rust is contagious and my pool if filled with stainless steel, I figure there's no harm in leaving the Culator in the basket to continue removing anything that may be leaching out. The Culator is capable of treating 25k gallons, and my pool is 3k, so I should be good with metals for quite a while.
As another thought regarding the old Nature2 I don't remember seeing the cloudy blue water when I dismantled the pool 9 years ago, but it's possible that I forgot. It was a long day.
It's a mystery. I could run it for another 10 days and check the filter, but now I have a Nature2 in there, and that will surely be the rationsle for the cloudy or blue water. I'm fine with cloudy blue water in my filter, as long as it's not clogging it, or getting into my pool, but it would be nice to know if it's normal or not. ...
If there were cloudy blue water in a sand or diatomatious filter, the owner would probably never know, because it would be expelled with the backwashing. Maybe it's just observable because it's a cartridge? I don't know how common cartridge's are in comparison to the other types of filters. Maybe they're only for small pools?
Thanks again. I really appreciate the ideas.