Hello
Bit of constructive advice from experience with the Mbu ( a well experienced fish keeper friend of mine)
When buying a Mbu, you should NEVER EVER just buy a tank that it fits in at the time, and then move it into a bigger tank, and then move it to another bigger tank and so on and so forth
You should start out how you mean to end with these guys
Imagine a thermometer, every time you move that mbu, the thermometer goes up a little, and then again when its moved to a tank, and then up again when its moved yet again, this is basically how their stress levels rise, and eventually it will end up so stressed it will stop eating and die
Their stress level will never drop back to zero of that makes sense
So moving ur mbu again and again and again is actually making it ill
Having it stocked with the fish you have also isnt good news, and yes you are over stocked. I would bet my left arm that the reason your puffer is ill is down to poor water quality
Im not being rude at all, im just making a few points
If it were me in that situation I would rehome EVERY fish in that tank bar the puffer and keep on top of water changes to keep the ammonia down
And ace, you were slightly mean, not every1 has the knowledge you do, so try and cut her some slack, weve all made mistakes before, no one is perfect