So, right before my lab started rearing squid, we were cycling our tanks and raising shrimp, etc. We have sort of a waterfall system on our three outside tanks (maybe 120 gallons each) and lids that allow the water to flow from one to the other.
Welp, at the end of the day, I must have bumped one of the lids, so the inflow was blocked. Wake up next morning to an email stating we lost somewhere around 100 gallons of artificial sea water, right down the drain. Water level was low enough that both our pumps and our heaters failed. If we'd had cephs in there, it would have been fatal. Luckily, the shrimp didn't seem to mind!
I now triple-check the tank lids every night to make sure none are occluding the inflows.