When to change DI resin?


A while back I changed all of my filters on my RODI unit and added a refillable DI canister with color changing resin. I also added a dual in-line TDS meter.

My question is- The color has completely changed on the DI but I am only reading 1 ppm on the TDS out. I am due for a 20 gallon water change this weekend. Should I change the DI, or can I safely let it go up higher before changing?

What would all the experts do?
I would bet theres some resin still active in the chamber, you could do the water change without any noticeable effects as 1 ppm is a very small amount. However, I would go ahead and change it if the visible signs are there.