for me, I would suggest to keep your hands off your tank and just enjoy it. If you had not added stuff to your tank, this would not have happened. If you go through the forums, you will see the trend, the majority of tank problems are related to overdosing something.
If the fish have a fungus, then should deal with the fungus, not dose the entire tank.
Even reading the OP you added flux, fraction, too much RO, then you "brought up" alk and mag, I presume with 2 different kinds of chemicals. Its way too much, its not the right way for a 2 month old tank.
I understand from your post you don't even have a rodi unit and still rely on outside water sources. Your priority is incorrect, rodi is one of the most important things you can have, while dosing is just the fad of today.
It is too many losses in only 2 months,you need to slow down, let the tank mature and settle itself, do more research, get better equipment (rodi!), get more experience.