i spoke to 2 other window cleaners (they where employed though) and they said go up to 100 but I stay at 002 and used to change at 10. but mine is at 15 and holding, I suspect the resin has gone.
my carbon filters are also moldy but I have new ones coming next week so will change the resin at the same time.
Next year I am changing to having a 40 40 and a hs5 in my van to make life a little easier.