I've heard much longer for fish, around 5-10 minutes actually. It all definitely depends on how well you setup for it (temp, ph) and the overall health of the fish. In most cases I'd consider a
FW dip to be pretty drastic for a fish, maybe not necessarily for some corals though. Either way you have to VERY closely watch what's going on and how the fish is tolerating the dip.
Sent from my iPhone using Tapatalk