Mhs has its limits to penetration depth as well. HAving a tank too deep, also means that light may not be able to reach the bottom. SImple case study.
When u go diving, or when u look from documentaires, have u notice that the deeper u go, it becomes dimmer?
3 feet depth tank? woah. U need a ladder to go into the tank to do mainatance. hahaha.
Cheers.