Paul,
A few things to take note of:
1) What is the temperature your chiller is set at? A 1 degC difference can cause a big jump in electrical consumption of your chiller. For my 3x2x2 tank, when my chiller was set at 26degC, my average daily electrical consumption was abt 22-24 kwh. When I increased the chiller temp to 28 degC, my average daily electrical consumption decreased to between 16-20kwh.
2) Your average electrical consumption for the 5 months is 576 kwh. Average daily electrical consumption is around 18-19kwh which I think is quite reasonable.
3) I would suggest that you take the readings from your electric meter daily for the next 1 week to see how much the daily electrical usage is. To be frank, I think using a 1HP titanium coil chiller would use much more electricity than your current artica chiller.