I will need to check it has been so long since building. I want to say it is 36” tall up under the tank. To make sure I had plenty of room to empty my skimmer cup.
Get a Craig Jig and drill pocket holes. Use all 2x4....no vertical braces needed. That will save you the width of the 2x4 on all four corners and it's a more solid build. Even then, I would still use a 40 breeder as it's going to be way more user friendly as far as any maintenance, etc. going on in the sump.
Following this as I'd like to build a new stand for my 120. I currently use a factory stand that came with the tank and with a 40 breeder sump I made I've never been able to remove the skimmer. It's pretty heavy with coralline algae and I'd like to clean it someday. Also, getting to pipe fittings and other sump items is a huge pain. I'd like to see what you come up with.
It is expensive but it can be redesigned to multiple sizes by just changing out a few pieces, can be dissasembled if necessary and may be the ladt stand you have to buy
I made the stand for my 90 gallon 30” tall and I didn’t have enough room underneath so I redid it as 36” tall and that is plenty of room underneath, but the tank is to tall for me to maintain without standing on something.
How much space are you going to have between the uprights to fit the 55 gallon?
The 55 is 12” wife if I remember.
You are loosing 10” underneath to the uprights.