Welcome!!! I also have a biocube, although just 8 gallons, and I have a heater in the first sump area, although lately have had some overheating? Maybe due to lights on extended periods. A word of advice- I have
fished (pardon the pun) 3 of my creatures out of the back, the sixline wrasse loves to jump in the sump, and today my percula clown was doin the up and down in the pump area!!! Luckily no worse for the wear, but cover the tank (when you get the fish) while you have the lid open!!!