I read on a different post about exposing the alcohol to a UV light. All the remaining resin is cured and falls to the bottom; afterwards the alcohol is passed trough some paper towels (as filter) to collect all the cured resin pigments and the alcohol is left like new. This is an awesome solution!
I experienced a similar thing. I used to have my cleaning tanks away from the light, but when I moved to a new office and placed the tanks next to the window, I noticed something “wrong” with the alcohol… it had now a white jelly that wasn’t there before. I removed some of that jelly, the rest has deposited on the bottom and the alcohol looks like new.