restarted pump, temps lowered

So I just had to turn the power off to the house for some home improvements. Since I've restarted the power my temps have dropped almost 15C! I've cycled the pump on many occasions before, but never have I seen this.

impellor may have been binding and not spinning - had the same thing on my 50z

That's the only thing I can think of too. Man, that's a lot of degrees to drop! I thought something was wierd with my temps too