I have a 60L tank - simple ... tank, fluval filter, heater, pebbles, 3 shells - been going for 5 weeks.
Cycled for 10 days, added 6 neon tetras (Bought at local garden centre), all seemed fine.
Left it for 8 days before I bought 5 Sailfin mollies (bought from Pet's at home) 1 1/2 weeks ago.
Also...