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    Treating an internal infection with metronidazole


    Treating an internal infection with metronidazole

    - Written by @myrasosweet, edited and formatted by @Alyssa


    • Important: Please remember that using a medication that your fish doesn't need, mixing incompatible treatments, or using the wrong medication for the problem can do much more harm than good. If you're not 100% sure what your fish has please make a diagnosis thread first and we will help you sort out the best choice to get your goldie back to full health.


    For internal infections, we suggest the medication Metronidazole. Seachem Metroplex is a popular form, but any will do. I've also found success in adding another antibiotic/antibacterial medication in some cases. These can include oxytetracycline, kanamycin, nitrofurazone, triple sulfa, and a few others. The following is a guide on how to medicate a sick fish and the items you will need:


    Items you need


    1. Hospital tank of ideally 10 gallons for ease of dosing.


      • Notelong and shallow totes supply better swimming space and surface aeration than tanks. They’re also cheap and readily available.


    2. A form of Metronidazole such as Seachem Metroplex.


    3. Airstone (when treating water), OR small HOB filter (when treating food).


    4. An ammonia/nitrite detoxifying water conditioner such as Seachem PrimeAmquel Plus, or Seachem Safe.


    5. Gel or Pellet food (Gel recommended).


    6. A liquid form of garlic such as pure garlic juice or Seachem Garlic Guard


    • Optionally, a binder like Seachem Focus may be used as well to help bind the medication into the food, particularly if using pellets


    If the fish has stopped eating, you will NOT need #6 or #7. Skip to the Waterborne Treatment section below.




    Food Treatment


    For most illnesses, Metronidazole is most effective when fed in a two-week course. Provide a hospital tank to ensure healthy fish do not eat the medicated food, and to monitor symptoms closely. Add a cycled HOB filter and change water regularly in accordance with water quality tests.


    Gel Food


    When using gel food, take the following steps:


    1. Portion out approximately one week’s worth of gel mix. This is about 7% of the fish’s weight.


    2. Add one week’s worth of the medication.


      • Metronidazole is dosed at one scoop per ten gallons every 48 hours. This calculates to 3 ½ scoops for 1 week.


    3. Mix in a few drops of garlic juice.


    4. Feed the fish approximately 1% of its body weight daily over the next week. If solid improvement is seen, repeat for another week.






    When using pellets, take the following steps:


    1. Portion out 2 days’ worth of fish food.


    2. Determine how much tap or tank water will be necessary to thoroughly soak pellets and place the water in a mixing bowl, beaker, or cup. Usually a few milliliters of water is sufficient, but different foods soak up water at different rates. It’s best test water on a few pellets to estimate the amount.


    3. Add a couple drops of garlic juice to the water.


    4. Stir in 1 scoop of metronidazole and mix thoroughly. If you are using Seachem Focus too, stir in a liberal amount of that as well (the directions suggest a 5:1 ratio of Focus to medication, I'm unsure if this amount is actually correct)


    5. Add pellets and stir.


    6. Refrigerate. Food is ready to serve when it looks solid.


    7. Make a new batch every two days and feed. Medicated pellets don't hold up as well as gel food and after a few days, they will spoil or the fish won't usually want them. If solid improvement is seen after one week, continue treatment for a second week.



    Waterborne Treatment Method


    If a fish has stopped eating or isn't eating reliably (spitting some food out, reduced appetite), use the waterborne method. This method is more complicated because Metronidazole needs to be re-dosed every 48 hours to remain effective.


    Important: If using filtration on your hospital tank, be sure that the filter contains no chemical filtration component, such as activated carbon, as this can remove medications from the water. Replaceable brand-name filter cartridges often contain carbon inside a floss bag, these also need to be taken out. A hospital tank may also be run without a filter as long as water quality is closely monitored 


    1. Fill the ten-gallon tank with tank or treated tap water.


    2. Turn on airstone for surface agitation.


    3. Add 1 scoop of Metronidazole.


      • Note: For serious or quickly progressing infections, Metronidazole can be double-dosed.


    4. Introduce your fish to the tank.


    5. Test your water parameters at least once a day.


      • Note: Until the fish begins to eat reliably, feed 50% of what is usually fed, and remove uneaten food. This will help maintain water quality.


    6. If ammonia levels reach 1 ppm or greater in 24 hours, make a 100% water change and re-administer the medication.


    7. If ammonia levels do not reach 1 ppm or greater in 24 hours, add 1 dose of Seachem Prime or your other ammonia detoxifying agent. Then make a 100% water change in another 24 hours.


    8. Repeat steps 5-7 for two weeks.


    Important: If instructed to use additional medications such as aquarium or Epsom salts, remember to re-dose it with each water change.

    Edited by Anna

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    (Adding an edit for picky eaters here! My little watonai just would not touch metro gel no matter how many tasty treats and flavors I added to it. Like any medication, it has an unpleasant taste and some fish just won't like it. She was however still eating so this is what I did for her)

    1. Portion out 1 feeding's worth of dry food, whatever they will reliably eat. I used NLS Thera A+


    2. Pour out a small amount of pure garlic juice or Garlic Guard into a small container


    3. Stir in 1/2 scoop of metronidazole and mix thoroughly. I highly recommend using Seachem Focus here, as the larger amount of liquid will dilute the medication slightly. Try to dissolve both as much as possible


    4. Add pellets and stir.


    5. Allow to soak for at least 10 minutes, then pour the entire mixture, liquid and all, into the tank. I highly suggest running a small filter on your tank for this to avoid tons of water changes. The remaining metro will stay waterborne which provides a bit of extra help alongside whatever makes it in with the food. Plus the yummy garlic cloud is nice and enticing.


    6. I found it was best to make a new batch for each feeding. It didn't take long, and she was much more willing to eat a freshly soaked pellet than a mushy day old one stored in the fridge. 
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