That's a tough one ... A 5 or even a 10gal I'd say should be ok ... but as Konvictkeeper said ... a 20 is at around 200 lbs with water, substrate, decor ... etc.
Unless you absolutely know it'll hold that weight ... you may want to go with stand in this case. Can you post any pics? If so can you do close ups of the legs? Maybe someone here has a similar table that can better comment.
75g Planted Barbs Denison, BlackRuby, Tiger, Albino Tiger, Green Tiger, Cherry, Gold, Checkered, Odessa.
NonBarbs Cardinal, Neon, RummyNose, Bloodfin Tetras, Z. Danios. 1RTS. Amano, Bamboo, Ghost & RCS. 20g Long Shrimp Tank RCS, Tiger, Amano.