Having a separate quarantine tank and quarantining new fish before adding them to your aquarium is definitely the most ideal option. However, setting up and running a quarantine tank is not always possible for everyone.
What I have found to be the next best option is to medicate the food being fed to the fish for 2 weeks when new fish are introduced. The Seachem Focus and Metronidazole are two excellent medications that are designed to work together and will help prevent and treat many of the common fish diseases and infections in your reef or fish-only aquarium.
Seachem Metronidazole treats many protozoan and anaerobic bacterial diseases: including Cryptocaryon, Hexamita, Ichthyophthirius. Seachem Focus helps to treat internal infections. When mixed with other medications and food, Focus will also make the mixture more palatable to your fish and will bind other medication to its polymer structure. When your fish ingests the food, the medication is delivered internally increasing its effectiveness and reducing loss of medications to the water through diffusion.
I have found pellet foods, frozen foods and seaweed flakes(available from TwoLittleFishies) to work best with the medication. Add 1-2 scoops of Focus and Metronidazole to the food along with a teaspoon of liquid food supplement or aquarium water. First, mix the medication with the liquid food supplement (or water) then add your fish food. Allow the medication to soak in for 15 minutes and you are ready to feed your fish!
When new fish are added, the existing fish in the aquarium will also get stressed. Feeding medicated food to all of the fish helps to prevent disease from developing and greatly improve your chances for a smooth integration. From time to time, fish will show signs of stress or disease due to poor water quality, drastic temperature or pH swings, aggression or other stress factors. This would be a very good time to start feeding the medicated food to prevent a disease break-out.
Marine fish can be very delicate animals. By taking a proactive approach, you can help to improve the chances of having new fish introduced to your aquarium successfully and keep disease at bay. As the saying goes “an ounce of prevention is worth a pound of cure”. Just as there are probably bottles of Asperine or Tylenol in your medicine cabinet, the SeaChem Focus and Metronidazole are two products that we would recommend keeping in your fish medicine cabinet.