Just curious to know if a wire hdx shelf which is rated for 350 pounds per shelf is enough to support a tank. there is currently a smaller tank on the shelf and that gives a slight bend so i am concerned about it. The tank is a 29 gallon tank too.
No. These wire shelves are strong, but not long term. Maybe 15 gallons would be safe, but anything bigger is trouble.
You would need plywood, 3/4 thick on each shelf with a tank, the wood would have to be the exact size of the wire shelf.
I used one of those in the 4' wide variety. I put four ten gallon tanks (racked end-wise) on three of the shelves. I did use a layer of 1/2" plywood on the shelves with the tanks. Even with the plywood there was about 1/8" of deflection (sag) with the weight of the tanks. That being said there was no problem with the shelf unit holding the weight.
One other thing, I did use two tie straps to the wall near the top of the unit just to be sure that it couldn't fall over (probably never would have but gave me piece of mind).