I've read about a few folks that stop doing water changes (or do them 1 time per year) when they start running a scrubber in coral and fish tanks.
I'm assuming those folks need to dose multiple things like Calcium, Alk., etc.; however, I'm curious what these folks actually need to dose????
Cal, alk, mag, maybe str.
If you don't feed nori, then dose iron and iodine.
Much evidence is also pointing to the need to dose Potassium. All the tanks I run scrubbers on have low potassium. All the tanks that I have tested that do not have scrubbers on them have proper potassium levels.
One of my original scrubber customers was dosing K (potassium) like mad, then he took the scrubber off to let the tank "get dirty" and his K stabilized. he put the scrubber back on and it started dropping again. So IMO the jury is in on this one. Test and dose K. In that order.