if it is 60/70 if one your own di only, but you already have an ro, if slow change the prefilters if they are 10inch will cost you about £4 ish.
I know a few rave about di only, I would di only if my tds was 30 but its 470 or more some times.
Ro comes down to 13 sometimes 11, booster 7/9 each of these better than di only..
I never did under stand why people use di after pump and or tank
If you have pure water in tank there is no need to carry the extra weight.
IAN