I said 30 minutes but it could be more than that I suppose but it's temporary. Normally I test both systems on the weekends - Alk & Calcium. Both tests combined take 10 minutes or less. If things are looking good, I only test NO3, Mg and PO4 once a month or so but I'm currently having some issues and that adds a few test a week to make sure none of my "Corrective actions" screw anything up.