Their are different types of DI resin along with different grades. There is color changing resin which changes color as it is spent to show that it is depleted and needs replacement. Regular/non-color changing resin stays the same color and you need a TDS meter to measure it's output and decide when it's time to replace the resin/cartridge. This is why some peoples resin is different in color than others. Even with the color changing resin I would still recommend using a TDS meter.