New Tank
 

I am currently in the process of designing my first saltwater aquarium, Tank and stand will both be constructed by myself. The tank measurements have been decided as 61"X21"X22"H. Out of 1/2 float glass. The frame of the stand will be constructed out of 2X4 wood studs. My question is for the bottom base would i be able to use 2X2 wood studs for the perimeter frame?

Yes.

I would agree as long as the floor is even.
Otherwise the 2x2 will conform to the floor and the top of the stand will eventually follow

My next question. Is it necessary to add cross bracing?

Let me clarify my earlier post.
I was commenting on the question of whether you were going to place a 2x2 or a 2x4 on the bottom of the stand. I assumed you were asking if 2" high or the 2x4 vertical, 4" high. It is the depth of the member that holds more weight if higher.
Try this:
Place a 2x4 flat with the ends supported off the ground and then walk on it.It will deflect down with your weight. If the same 2x4 is put on edge, your weight will not deflect it.
If your basement ceiling is exposed, I would install cross bracing. When weight is placed on one stringer on the floor, some of this weight will be transferred to the next stringer on either side. This would be most helpful at either end of the tank.
This is assuming your stringers in the floor are at 90 degrees to the length of your tank.
But I am not an engineer, who could tell you for sure.

are you going to skin it out in plywood?

maybe do a sketch of want you want to and post it for feedback.

also maybe search for plans on the net for ideas.

Sorry. i should have been clearer on my last post. I have decided on the framing of the stand and will be skinning the stand. My question was about the DT itself. I have seen tanks with euro bracing but that would interfere with my light mounting. I am curious if i should put cross bracing across the top of the DT. the glass will be 1/2".

all things considered over build for piece of mind. the extra in wood for some cross bracing etc is well worth it