I agree with Mister Sparkle, ammonia.....in a 2g container the ammonia can start to rise in 3 days provided that the fish was not over fed and all uneaten food was removed after feedings.
Without filtration or some source of aeration you will not get a true cycle per se', regardless of aeration in that size container more water changes are needed as Mister Sparkle posted.
IMO/E-2g needs at least twice weekly 50% water changes with a filter and without filtration water changes need to be one 50% and one 100% weekly to provide quality water and prevent most illness and fin issues......
As stated.....water change, water change..etc......