Will my stand be strong enough for a 210 gallon?

[Newfe]

Support the frame in the same way as the picture. Lay the 2x4 on the bottom and directly under the top. That way its support is solid.

 

[Pharaoh]

As suggested, just turn the vertical supports in the center. You will be able to get 4-5 extra inches worth of room in the middle.

 

[Paulbearer]

If you click on the link in my signature on my 180 build, you will see what I did. I have a 55 gallon under it right now running as a sump and it was easy to get in and I can get it out also from the back or side if needed.