We tried one of the shelving units. My hubby tested the weight on them and the steel shelf would flex with him. So we are going the 2x4 way, makes me happy.
We done some measurements the shelves will be 7 feet long, and 20in wide. Height to be later determined, about will be around 72 inches high give or take. Plan to leave a 6 in gap from the top of each tank to the bottom of the 2x4 that makes the next shelf. Should be enough room, we'll test it out as we build. I'm hoping to get one shelf made this coming weekend when he's off work.