so if it still works ok at 10/15, when its time 2 change fillters do u do them all at once,
so u know where u r with everything ?
When your TDS rises above zero, which if you use a back pack, will be some months away, then change only the resin and you'll find it's all okay.
I change my pre-filters about once-per-year if I'm lucky, and I change my RO filters when they're knackered (but my first lasted me about three years). I knew they were knackered because I had to change my resin after about a week, when usually it's a couple of months.
Don't forget to flush your RO filter at least once a week. If you don't know how to do this (it's ultra simple) post back.