I try to get all of the outdoor tasks out of the way. Things like cleaning saltwater mixing vats and anything requiring a hose. I put a moving blanket over the aquarium hood, to keep heat in. Check all the heaters and test the heating system. Especially paying attention to if heaters in each tank are keeping up, during the not so cool nights. In my 120, I have a heating cooling redundancy channel set up for summer, which gets swapped over to a heater in winter. Thank you for reminding me, I need to do that. Checking the Alk more often as windows are closed, which effects daily PH swings, which in turn has a direct correlation on Alkalinity uptake. Coral take in less, at lower PH levels. Which also reminds me, need to calibrate the PH probe. Those are most of the things I pay attention to.