I`ve got a 180 litre tropical tank in my room with just your general tetras, mollies, a plec and another kind of cat fish kind of thing which I can`t remember the name of. A did have a bala shark which grew to about 6 inches long but he unfortunately died earlier this year

He was ace but my god so scared of anything, heard him trying to jump out of the tank numerous times in the middle of the night
Just scanning though the thread reading about new tank syndrome and cycling. I just put a few neons in after a couple of days of the the tank being set up then did 1/3 water changes every couple of days and never had any problems.
I`ll get a marine tank one day when I have the time.