It is too late for me, but any members keeping Koi outside should check to see if their de-icers are working properly. Deep snow prevented me from seeing if I had an ice free area around my de-icer. When I was able to check again a couple of weeks ago I noticed the my GHI had tripped. Result: The four largest fish I kept outside were floating at the surface and obviously dead. I have a few more fish in this pond, but the water is too clouded to see the others.
Tony Vaquero

We are all sorry to hear of Tony and Ann's loss.
Because of the existence of electricty and water and the outdoors, it is necessary to use ground-fault circuit-interrupter (GFCI) curcuits. Please be aware these can trip very easily causing loss of heat, pumps, air, etc. Also, they can be prone to failing in the "power-on" state and should be tested every couple of months.
Doug