es its physically possible but not likely, the majority of common computer desks are made of particle board, not exactly the best material when it comes to aquariums. I would just either keep your eyes open for a used one on here or cl or perhaps build a basic one
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Crap I gotta pay better attention, if its an actual desk made out of solid wood, yes you could prob use it, if its a computer desk, follow what I said above.....only problem I've experienced is that desks usually aren't built with weight-bearing in mind. A 40b is roughly 350 lbs and that's just water, not including lr sand and tank weight....so I'd be careful