Well, 50 US Gal of water is = 417.2632055 Pounds OK, 417lbs.
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Online Conversion - Water Weight Conversion
That is not including the Tank, Gravel, Rocks or other stuff. Not knowing what your furniture is rated, I would be very worried about that kind of weight (over time) causing the support to weaken and possible wiggle side to side. (I know many Pre-Fab) TV/Stereo stands will get that way after time.
Maybe someone else will jump in and give some info that may help. I will be setting up my 55gal soon and I will rest easier knowing it is on a Iron Stand.
Later, Pop's