That is around 1k gallons, so 2k - 3k watts of heat depending...
What does it depend on?
Ambient Temperature
Is it covered?
Is it insulated?
How much above ambient do you need to heat the water?
My 400g pond in my Garage has no heaters currently, I pulled them all about a week ago. It's been sitting right around 80° all by itself... So this time of year, you don't even need them really. In the winter you will, but if you can heat the room the tank is in then you can skip heating the tank. It will likely be cheaper too, having 2k + watts of heaters running would cost a pretty penny no matter how cheap your electric is...