I didn't say this to @atoll cause I know his tank is super mature and with an oxidator, but for the rest of us impatient mortals gas exchange is key for butterflys. If you think you have enough gas exchange triple it and you may be close.I’ve always loved all butterflyfish .
the first impulse fish purchase was a blue spot ( impossible to keep in captivity )
Klein was infested with ich only a day after adding to my system .
red tail didn’t eat
raccoon hid behind the rocks and never ate
Fast forward to present day . If I ever choose to do a fish only system I would consider trying butterflyfish again
Also, I have come to the conclusion that gas exchange is for primarily CO2 exchange. This means your room CO2 needs to be low. Alternatively skimmer plus outside line. Pretty much everything you would do to try to raise your pH is what you need to get butterflys to go.
FWIW.