FWIW I have used Erythromycin multiple times on my tank (mainly to treat BGA). It has NO EFFECT on the biological filter. No amonia spikes of any kind. I would not hesitate to use it if the need called for it. Just follow the directions and treat for the full duration of the treatment when using it.
It gets rid of BGA without any issues. Never saw it affect shrimp in any way either.
Only fauna that seems to be affected (that I can tell) is malaysian trumpet snails. After 3 seperate EM treatments, my MTS population doesn't exist anymore. Not that I really mind
.