thats a good question man.....
OK... remove the circuitboard and tube and all that junk and then calculate:
I think 21" old crt weighs about 60lbs so, 55lbs of thats tube, wiring, boards.
plastic shell = 5lbs
new tank glass (flat screen of course)
and water est 8 gallon capacity plus other stuff, minus rocks water would be approx 6 gals, 6x8=48 plus glass est 10lbs plus rock/sand maybe 40lbs?
Sooo.. probably around 100 lbs?
Hehe... the stand would probably do it but might be not that trustable.
A reinforced stand would be in order huh!