My Tank crash - Hopefully you can learn from my experience :(

[hfp75]

I don't trust check valves either, but some tanks require one & they need to be acid soaked frequently to ensure they are clean...

[rsisvixen]

I agree, seems fishy (pardon the pun)
We were without power for 66 hours last year, my temp dropped from 26-22 over a period of 12 hours (this was in fall so ambient temp wasn't too cold )
Since then we've had another 3 power outs (gotta love these windstorms) and I've had the tank dip to 15 over winter-everything made it through no trouble. As long as the change is gradual your livestock will adapt.