Tropical tank help please?

doing a true nitrogen cycle with fish is very stressful on the fish themselves. you're doing well by keeping the ammonia and nitrites down with water changes, keep that up. the unfortunate part is due to the stress on the fish, losing fish during a cycle is common and there's not much you can do about it short of cycling the tank with liquid ammonia before adding fish. overall the process can take up to 6-9 weeks.