Why does my red-eared slider’s eye water after applying erythromycin ointment?

Hello. Based on your description, the turtle’s eye watering after erythromycin ointment is likely caused by the eye problem itself, not the medication. For example, if the eye has a bacterial infection or pus, watering can occur. There are many causes of eye swelling, and different causes need different treatments.

For now, dry-dock the turtle and apply anti-inflammatory eye drops or ointment to its eyes as appropriate. If symptoms keep worsening or are joined by others, seek veterinary help.