Did you say 520Liters? ok ... that's about 137 gal
... lots of stuff you can do!
Sure you'll get tons of suggestions ... oh boy! How about a big Barb Tank!! You would easily double my stock (see below).
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.