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API E.M. Erythromycin

$ 49.00 until FREE shipping

We now prefer using Maracyn as it's the same active ingredient(erythromycin). The price of API Erythromycin keeps going up multiple times a year. Maracyn has remained a better deal.

This is what we use here at the store and at Cory's fish room to treat every fish we come into contact with. For us we've never had problems using it with inverts, scaleless fish, and plants. We've never had our beneficial bacteria die from this medication, but as with all medications take precautions in case your cycle does crash. 

Commonly used to treat:

  • Cyanobacteria
  • Fin Rot & Tail Rot
  • Columnaris 
  • Open Wounds

Dosing Instructions:

For best results remove activate carbon. For each 10 gallons of water empty on packet directly into aquarium (For 850gm jar, add one scoop [1tsp] per 20 gallons), repeat dose after 24 hours then change 25% of the aquarium water. Repeat treatment a second time for a total of 4 doses, then make a 25% water change. Treatment may be repeated if necessary. Four doses required for full course treatment. 

Treats 100 Gallons. 10 Packets, each treating 10 gallons. 850gm container treats 3270 gallons.



Customer Reviews

Based on 66 reviews
Skin Infections

Worked really well for skin infections on my cardinal tetras

Fin Rot

Works really well. I readily keep this med on hand. Have seen great success in treating fin rot with this.


Just keeping for inventory. But I bought the wrong brand. Should have bought the Maricyn and saved some money. Didn't return it though cause it was my bad not Aquarium Co-Op. Cory can buy a few more tacos now. Works well though since I have used it in the past. Good delivery.


I like this medication. It works well. It’s similar to Maracyn. I’ve used both with great satisfaction. I would recommend either product.

Can't go without erythromycin on hand!

This stuff works wonders. The med trio that Cory suggests is the absolute best thing to happen to my fish keeping hobby in years. It covers just about all the common stuff and it's super easy to use. We don't place a fish in any of our tanks until it's been through QT with the med trio. Erythromycin is a huge part of the trio taking care of the bacterial infections the commonly plague stressed and recently shipped fish.