I first kept rays about 10+ years ago before taking a break for school and life in general. Had a couple of motoros that would attack every fish in the tank, lost a lot of nice fish to them lol.
I'm back in it now and had my potentially worst mistake yet. I heat my system off of my water heater, pex coils in the sump. Well the temp probe came out of the water without me noticing, over the course of about 24 hours it raised the water temp up to the high 90s, highest temp I saw was 98*. Reason I noticed was because the rays weren't very active and weren't eating much. So I started doing my checks and realized how warm the water was. Found a second thermometer, dropped it in and saw what it was at.
That one scared me a lot, I thought I had killed my P14s. They were off for a few days, not eating a whole lot, but they are back to normal now, eating like pigs and terrorizing the other fish in the tank.