OK no added Co2 but to get results like that you must be adding something, I've just started using Easycarbo and Profito I'll be happy if I can keep my plant alive!
https://youtu.be/o1BwdkYUvlMQuick update video. All the cardinals added now. Nothing left in quarantine.
I'd go with more tetras and see if that brings the corys out.Since I've had the emperors the C048s come out more.....
Remember that goldies will eat smaller fish.The warmer the temp the quicker the metabolism, so, for growing-on fry I would suggest it's not a good idea for the development of all the internals.