Personally I use an Injector system for my
nutrients and I run nutes 5 days a week every time it runs then do plain water 2 days. I've run nutes 7 days a week vs the 5 days and haven't been able to tell any difference in the crops and it saves me on nutes. I grow in coconut coir.
In my recirculating system I run the nutes all the time as it's easier then changing tanks where as with the injector board it's just turning valves