Mitch has the right idea. Composites and laminates are great for important structural components (like long spanning unsupported beams). Regular lumber is subject to grain and knot imperfections that create weakness. Of course you can always just beef up the lumber, but then you're losing valuable opening space into your sump area. I built my stand out of 3/4" oak ply, solid panels all around taking the load with a double-thickness laminated front panel that was cut away to allow access for sump etc. The laminate nature of the plywood with alternating grain direction make for very strong parts. I've got photos and solid models I can share if you like, but my particular design probly won't help much as it was designed for a tank that's 30" x 24" x 24". If I were doing a stand for a tank as long as yours I would design it with a support mid-span (front and back) and make the front support removeable. I have seen clever ways to take the load off the front-center brace of a stand while a sump is being serviced with a full tank still in place.
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