My thought is to double the 2x4's on each side rail, deck screwed and glued, to make one beam for each side, skinned with 1/2" ply. Should be enough, ya think?!
Dual 2x4's on each side should be plenty. The common 2x4 stand posted around a lot of the forums has single 2x4's on each side spanning 4 feet. Dual 2x4's glued and screwed would be much stronger. My architect friend has always encouraged me to use extra fasteners in the beam. He says you truly have to make it "one" in order to get the strength advantage.
The 1/2 inch ply wouldn't provide strength but would keep everything together, a good idea IMHO.
If it were me I would probably throw a cinder block in the middle of the beams, but I over build everything. (My beam in my basement called for two 6" beams. I went with three 8" beams)
Hey Suds. Yeah, my projects tend to go like that. Like I always tell my wife, I don't pretend to be an engineer or carpenter, but if I build something you can bet your arse it ain't gonna fall down!! LOL..Material is always cheaper than failure.
All of the tanks in my fishroom (50+) are on 6" cinderblocks and 2x4 and 2x6's (for up to a 4' span). I've got tanks ranging from 10g to 150g set up this way (for the past few years).
I just stack the blocks and lay the wood across the front back and middle. Don't try to overthink it.
I use a layer of styro under the tank to level things out.
Hello Dog. Western Md, Washington County, 5 miles west of Clear Spring, in the mountains, in the woods. How bout you?...Nah, ain't trying to overthink it really, just picking the herd's brain. Never know when you'll pick up a useful tidbit that you didn't consider. I'm only running 4 tanks right now, but I'll be setting up the 5th once the new fish room is done in a couple weeks...hopefully. 40 breeder, 56 Oceanic and 3 75's. When I bought the 5th tank the wife threw me and the fish out of "her" house, so hi-ho, hi-ho, it's into the garage we go!!....Merry Christmas to all you folks out there