DYI Stand Plan, how is this idea?

[daplatapus]

Monocus is correct. With a 75 gal, 48" tank, 2X4 is fine. But being a contractor and seeing literally 100's of studs a week, I certainly would want to personally chose those that I would use. I can't believe the crap their allowed to sell.
I would also lose the Blue joist as it's really not necessary and just complicates the design.
Just make sure when you're laying out the joist spacing that one isn't where your holes in the tank are. And keep the joist to no more than 16" centre's.
I personally don't like using pocket screw for anything structural. If the stand is being skinned or covered in any manner, those screws will be hidden anyway. In any floor joist application, if you can end nail ( through the rim joist at 90 degrees into the end of the joist) you don't need hangars.
As far as doubling up the front rim joist, it potentially has it's merits. In the back, you're more than likely going to skin it or even put a stud midspan to help carry the weight. But in the front, if you have a sump, you may not really want anything preventing you from slipping a sump in there or at the very least have a support that's removable so you can do so. The limit there though is (if that's why your putting it in there) you really shouldn't remove it while the tank above is full. It's only on set up, before the display is filled, that it can theoretically be safely removed.
In this case, a stand builder may decide for extra insurance, and to help strengthen that front support, instead of putting a stud mid-span, to double it up.