You could get some magnets from somewhere such as Lee Valley Tools (rare earth ones are great for this - little hockey puck-shaped ones)
Glue the magnets
into one surface, and screw in some fender washers on the other surface. Then you can use whatever covering you like ... Ikea doors, something from the Re-Store, used kitchen cabinet doors from craigslist, make your own, or whatever
Nice job on the stand BTW
I don't wanna scare ya, and maybe I'm wrong
I don't want to knock your woodworking skills, but if that stand were mine ... and maybe others will disagree with me ...
If I were to build a stand for a tank that'll hold a 1/2 Ton of water, I'd want more support for the front and back long sections. Maybe it's just me, but I wouldn't want the bottom glass being the only support for all that weight. I can picture the stress of the weight causing the bottom to bow down in the center
I'd want either center supports, or sistered 2xs
Thinking about weight distribution, you're asking each of those 2 2x4s to hold 250lbs of water in the center, aside from the glass, sand and rock weight
As long as you're comfortable with this, carry on
Hopefully someone else will chime in to prove me wrong and assure you all is good
Keep those build pics comin'