Sorry for reviving a dead thread but isn't changing the filters because your TDS is 1ppm excessive? I thought anything under 10 TDS is still good. I obviously understand that 0 is better but If I can get a few more months out of my cartridges with no harm to my tank, why should I change them? Just curious.

On a side note, alexdmg has one of your units and it's awesome. I may plumb one into a line in my house and run it into my top off container. I'll look you guys up if I decide to.