Mag-7 heat dissipation

I just picked up a pair of Danner Mag-7 water pumps. I'm planning
on using them in parallel redundancy on a 180G tank I'm setting up.

To test them I placed them in a 5 gallon bucket filled with water
and turned them on overnight. The next morning, to my horror, when
I placed my hand in the bucket to feel the water flow I just about
got burned. The water was VERY hot, well over 100 degrees.

Does this sound right?

I know they're supposed to dissipate SOME heat into the water when used
submerged. And I also know that the problem won't be so bad in a 180G tank
compared to a 5G bucket.

BUT THAT WATER WAS HOT!

I'm starting to worry about poached fish.

ADVthaAnksNCE