yes the softner is brown , should have a sticker on the left hand side saying its the softner, the carbon one is dark almost black, definitely change your di cartridge for a vessel which is much more economical.
i was going through a DI cartridge every 4- 6 weeks @ about £70 +vat +delivery, now i use one bag of resin every 10 months @ £70 a bag.
you will also need to flush the membrane weekly, can talk you through this if you get stuck
greg