When it did not have the centerpost, it bent for less than 1/8 of an inch when i filled it up . Then i added the centerpost, The tank on the bottom was supposed to be a filter but eventually became a show tank, hence now I want to move the centerpost 10 inches to the right.
The stand is made from 2 inch angle bar, 1/4 inch thick.
Here are sets of pics based on what you posted. It's basically a beam (the table top) with three columns (legs.) I'll ignore the bottom part since without pictures, it's only a guess what it does. It likely is at least partly as a stabilizer for the three columns.
I assume the 3 columns are equal in size. Is that true?
Also, I am no engineer.
The first set is your picture with the show tank removed and your added angle supports removed.
The second is edited to show the point I want to make.
Imagine the left column has been removed. You now have a cantilever. However, the original (on the left) is substantially less weight as an overhang than the proposed one (on the right.)
In the original, the left column was asked to hold much less weight than in the new version. The stress that has to be addressed is the new additional loading on the left column.
How much? I don't know. Was it over built (columns are far stronger than any engineer would design) or was it built to have a reasonable safety margin? Would a bracket (as you added to the middle column) make the modification feasible? I don't know.
What I would do is add more column support on the left. The bracket is not a bad idea, but it may not be sufficient. Brackets are typical as a solution to cantilevers, but the cantilever will still fail if the bracket is insufficient or the column is damaged from the bracket itself. (I had one fail suddenly with a pile of books while I was a student in Chicago.) It didn't bend or droop for weeks, then in 1 split second it went.
With added left column support and a bracket I think it would be as strong or stronger than the original. But again, I'm no engineer, so by no means am I arguing this is correct. Just my $.02.
