Looking for advice on heating tank with RKL

[GoFish]

I have 1 150 watt heater in the display controlled by a reef keeper lite. It's set to 77.5 with a +/- 0.3 hysteris. Currently the tank is sitting at 74.4 and with the cooler weather and rarely having the heat on in the house the heater is pretty well running 24/7

Any advice on how to up my temp?
Higher watt heater?
Second heater? If so can it be controlled with RKL? (there is 1 empty plug in)

Tank is 46g with 20g sump = 48g water volume

Thanks in advance!