Imo no you dont need a di chamber its more of marine aquarium thing I think but dont know 100% but basically the di chamber comes into play if you have a high tds and want very low tds water again I think im right in saying as a rough example, an ro unit should remove around 95% of input so if you have tds of 400ppm after the ro membrane you should have around 8 -10 ppm the di chamber should take this down to zero,
Thats my understanding of it but I might be wrong