It's not absolutely necessary. We don't have one. You may need a fan though.Do you have a canopy or is it a pendant? Canopys are good cause you can install a fan it it. Pendants are good cause your system has plenty of air flow above it.
It's the Aqualight Advanced system I am putting it under my existing canopy. I have the top opend for airflow and the sides of the canopy I put egg crate as a look instead of the sides of the canopy wide open for air flow, also the back is open. I also have egg crates going on the tank in place of the glass tops.