Simply Koi and More Koi

Hi all, I have a 2000gallon pond and i have a 2kw in line heater as i thought it was one kw per 1000gallons much the same as u/v's. I have not used it this year as my bill last year was costly. But i did run it 24/7 at 12c so it was going on and off as the temp dropped etc. I also coverd the pond wi...