What’s in API’s EM Erythromycin?


Active Ingredients: 200 mg Erythromycin per packet.

Note on Erythromycin: Erythromycin is most effective against gram-positive bacteria, such as Streptococcus species. The vast majority of bacteria that cause disease in fish are gram-negative, so erythromycin should only be used after culture and sensitivity test results confirm it will be effective. Also, erythromycin is not very effective in a bath treatment, and it should only be administered by injection or in feed. Erythromycin is not FDA-approved for use with food fish. (Reference

What's in API's EM Erythromycin
What’s in API’s EM Erythromycin

Labeled as a “Broad Spectrum” antibiotic, that’s not exactly true. But people still like it anyway. 

Directions for Use:

For best results, remove activated carbon or filter cartridge from filter and continue operation.

For each 10 gallons (38 L) of water, empty one packet directly into aquarium.

Repeat does after 24 hours.

Wait another 24 hours then change 25% of the aquarium water.

Repeat this treatment for a second time, for a total of 4 doses.

Then make a final 25% water change and add fresh activated carbon or replace filter cartridge.

Treatment may be repeated, if necessary.

This package treats up to 100 gallons.

Four doses required for full course of treatment.

What’s in API’s EM Erythromycin


Dr Erik Johnson is a Marietta, Georgia Veterinarian with a practice in small animal medicine. He graduated from University of Georgia with his Doctorate in 1991. Dr Johnson is the author of several texts on Koi and Pond Fish Health and Disease as well as numerous articles on dog and cat health topics.