The problem with a leveler foot is your are now putting the entire weight of the tank on "x" number of points. The whole idea of that bottom 2x4 (I used a 2x6) is to spread the weight of the tank out over the entire length as much as possible.
Say you put a leveler foot down, and due to spacing of the floor joists it is dead center between 2 joists. You now have the weight of the tank pushing down on a point that is 7" away from any support. It will not fail right away, but over time that floor will start to sag & your tank will become unlevel - possible leading to leaks.
The only good place for feet to level a tank is on a cement floor IMO. And I would still go to the "trouble" of making a level stand without feet