I have seen the introduction of a BP reactor strip too much nutrients out of a system too fast which can cause a shock effect. I havent experienced shock in removing BP reactors. I would caution shutting down one if for only a short time. Doing so can kill the bacteria on the pellets in the reactor...and could likely create a nasty smelling and outright putrid situation. Don't ask me how I know... Suffice...it was an experience I don't like... re-living. When you fire it back up...and the smell hits you, it is too late as the contaminated water is already in your system. Removing some pellets is an ok approach. I have taken three offline with little shock.... what I saw was tanks that seemed to suddenly pop...