Any comments?
Yes, check your refrigerator. Is it running... you better catch it 

Really do check your fridge. Place a dollar bill between the door and seal. It should be hard to pull out. Check for any new crimps/wrinkles in the gasket seal. Our bill jumped up about the same time I started up my 125. My wife argued that it was the tank (I arqued that it couldn't be), and an investagation revealed that the kids had turned down the temp on the fridge/freezer and the door gasket was shot. After changing the door seal and turning it back down to where it should be, our bill dropped back down to normal (I shouldn't admit this, but it took me about 3 months to get around to finding the problem... it was only after my wife threatened to pull the plug to the aquarium).
Your electric bill shouldn't hardly notice a 55 gallon tank with two N.O. bulbs and, I'm guessing, a moderate pump... $5/month off the top of my head. Too lazy to calculate.