My RO/DI is pumping 2-3 TDS now and I can't get it to zero. The RO has got about 6-7 TDS coming out of it, so I guess it's my DI that's spent? Should I change it now or wait till it's doing nothing. I'm really thinking that I should change it ASAP before I start getting red slime and green hair. Wait... too late. Stupid question, I know....