No, you can place as many bulbs you want over the tank, if it's wide enough and the fixture fits within the tanks' measurements.
I would think your tank is 24" wide (?). If so, it's a shallow tank! The tek fixture (19 1/2" wide) will fit and still have room.
The combination of bulbs will depend on you.
I would suggest 6 Blue Plus bulbs and 2 "white" bulbs. You could choose 10.000Ks, 15,000Ks,…
Do you have a plan for the bulbs? Let us know and we'll try to help you out.
Tek is a simple fixture and works great.
They don't make them anymore.
I had Tek in the past and ATI fixtures also.
Grandis.