I have had my tank up and running now for about 4-5 months and have been doing regular water changes and also a 1-3 gallon top off everyday. I occasionaly check my RODI water with my TDS meter and it normally reads zero. I just tested it a few days ago and now its reading 10. I was wondering which cartridge or whatever needs to be replaced first. My sediment one is looking kind of light brown in color. Here is a pic of my setup - the resin is not mounted on top like in the pic - I changed that before it ever got used much. Thanks for reading and in advance for the help.