I did think the same myself but i followed advice from here and was told to add more of the bh tetras and cardinals and corys and I wouldn’t be overstocked but I did think it wasI think a couple of buddies for your lone ADF, I can't remember how many of each of the others you had before but if you liked what you had maybe more of the same?
Edit - you have a similar size tank to me, I'm wondering if overstocking may have contributed to the issues you've had? I know you've lost quite a few but can't remember how many you had originally.
I’m kind of leading to a few shoals of tetras
But I don’t think I’m over keen on the bh tetras as they seem to have been aggressive to each other since putting them in