I notice you're using 2x4 for the framing, you should consider adding some vertical support pieces to the back connecting the top frame to the bottom. I know you have the 4x4 legs but the top frame being 2x4 makes me a little nervous. Other than that I like how everything is turning out so far and will be following along.
Thanks ti floyd suggestions, my son and i was able to weld the bottom with very little bubble that i can count with my fingers.
Here is the pics of the seam and the completed tank.
Not much update lately, i have been busy with work. But also take me a while to paint the background. I painted 4 coats, so pretty much 4 night right there. I also drill 2 holes for the over flow.