There is a lot going on under the tank. A sulfur denitrifier sits on the left. There is also a phosphate reactor and the intake side of the sump The output side of the sump can be seen on the right along with the battery backup and the AC monitor - that notifies me if there is a power failure.
  
The Controller (an Aquacontroller Jr) handles all the regulation events (lights, circulation, automatic dosing) and displays the time, what is on or off pH and temperature. It can stop all the pumps during feeding or water changes and it has made maintenance of the system so much easier.
On the right is another picture of the AC monitor (that I built). It notifies me if the power fails and when it comes back on. This one also controls some pumps based on water levels
  
The Kalkwasser reactor sits under the refill tank. It adds calcium to the make up water and increases the total alkalinity
On top are the lights. I have finally settled on 4 T5 lights that I change about once a year.