It depends of many factors: how thick substrate is, how old is it, how many shrimps you have per tank, how often and what amount are you feeding, what food. Most important what filtration. I use to do weekly 20% WC with RO and Mosura mineral+ thru peristaltic pumps 5gal for 3h .My shrimps have been dying no meter what I have been doing. Now after 1.5years of experiments I’m on 12% monthly WC-almost no dead except some new born and old shrimps. I have 6 neo tanks,5 CRS/CBS,4 tiger tanks,4 TB ones. WC is the same for all of them. You have to find your sweat spot for maintenance and feeding.