When Do You Change Your DI Resin?

[reefermadness]

I dont bother to use the colour changing resin...it costs more and is useless if you are using an inline TDS meter.

[Mike-fish]

Being on well water with high iron I burn the di resin in no time for me I have a tds of 1 it will hold there for a while then sky rocket I change it when it does so. Even with that I've gone through 5 cartridges in as many months.