Recently reused coco for the first time. Flush well and like others have said, using an enzyme to break down old roots. So far everything is great! Have some clones/soon to be mothers in reused coco and they are doing fantastic!
I'm on the same coco for almost a year.
Do NOT re-use coco! I've just wasted 6 months (almost two full grows) doing it. The first full grow was a disaster, the bud tasted disgusting and the THC was almost non existant... Stupidly I re-used it again and got about a month in and chopped the lot...
Bought two fresh bags and started again and they are growing rapidly, I will never re-use coco ever again.
For the sake of £20 it's not worth it, just buy new bags and save yourself a nightmare!