I believe you only need to do a half dose of Maracyn, (erythromycin), to get hopefully get rid of the red slime--otherwise known as Red Slime Algae (Cyanobacteria), so it shouldn't have a huge impact on your fish. But I understand your concern so perhaps wait a few weeks before you do the erythromycin. In the mean time keep up with the manual removal and plenty of partial water changes. A fine mesh filter placed in your regular filter may help to filter some of it out although you'll need to rinse this filter out often to actually get rid of the algae.
Running a diatom filter for a few hours will also help to catch any free-floating algae.
Good luck with it.
Robin
Running a diatom filter for a few hours will also help to catch any free-floating algae.
Good luck with it.
Robin