For our full, in depth four page internet page Aquarium/Pond Medications page, please click on the picture below:
Including Separate pages for:
Antibiotics/Antimicrobials, Chemical & Parasite Treatments, & Organic Treatments

Further Recommended Reading:
Fish Diseases | How to Treat Sick Fish
TRUE Aquarium UV Sterilization; How to Use a UV-C Sterilizer

Aquarium Information
-A great source for current aquarium information that is updated regularly as new research become available.

Metronidazole; by SeaChem, API, More


SeaChem Metroplex, Metronidazole Revised 1/16/19

Metronidazole is an antibiotic (for anaerobic bacteria) and anti-protozoal medication used to treat various conditions internally and externally in fish.

As for Anaerobic bacteria, these are bacterium that thrive in environments in which there is little oxygen (anaerobic environments) and can cause disease in such environments as the intestinal tract and liver.

Metronidazole belongs to a class of antibiotics known as nitroimidazoles which work by ceasing the growth of bacteria and protozoa. Metronidazole works by selectively blocking some of the functions within the bacterial cells and some parasites resulting in their death.
Metronidazole is metabolized in the liver (whether a fish or a human).

Metronidazoles primary use is for the treatment of ANAEROBIC gram positive & SOME negative bacteria including those that produce beta-lactamase.
However, it is not effective against aerobic bacterium. This means Metronidazole is a poor choice for suspected bacterial diseases in open heavily oxygenated aquariums/ponds such as Columnaris, while it is an excellent choice for diseases of the low/no oxygen environment of the intestinal tract or other internal suspected bacterial pathogens (generally used ina fish food soak for best results).
Metronidazole may be a good choice for any bacterial disease present in low oxygen, high bio-load aquariums or ponds.

As well Metronidazole is effective for some protozoa.
It was originally found effective for the management of infection caused by Trichomonas vaginalis.
For fish applications Metronidazole has been shown to be in particular more effective for internal and external flagellates.

Metronidazole is also sometimes effective for other protozoan parasite infections, especially for Cryptocaryon in marine aquaria as well as Hexamita & Ichthyophthirius.

Metronidazole is often recommended for disease in Cichlids which is often thought to be caused by Hexamita, HOWEVER there is considerable evidence that the cause of "Hole in the Head" is simply the lack of Calcium and even positive calcium ions. This is especially common in aquariums utilizing water softened using sodium chloride or potassium chloride to drive out hard water minerals.
Use of such water should be ceased prior to using Metronidazole and as well, the use of products such as Wonder Shells mineral blocks should also be used first before treating with Metronidazole (or combined).
Hole in the Head Disease
AAP Wonder Shells; Unique Version

Due to Metronidazoles effectiveness against anaerobic bacteria by selectively blocking some of the cell functions of anaerobic bacteria, Metronidazole along with Neomycin is a good choice for bloating of the digestive tract (common in goldfish).
Metronidazole selectively blocks some of the cell functions in anaerobic bacteria, resulting in their demise.

Metronidazole is also effective used in combination (such as with Praziquantel) or by itself for internal parasites such as Nematodes or Trematodes.
In marine aquarium infections is where Metronidazole really shines as it is very effective internally and since Marine fish are always drinking the water around them, medication is easily transported to the infected area.
In Freshwater, treatment can be improved by soaking food as well and this is still an effective freshwater treatment as well.



Directions from SeaChem Metronidazole; use 100 mg. for every 10 gallons (40 L).
Repeat every 2 days until symptoms disappear.
Make sure any UV Sterilizer (if used) is turned off and any carbon, Purigen, Chemipure or similar chemical filter media is also removed during treatment.

To feed (use as for a medicated food), use 100 mg. with approximately i tablespoon of frozen or dried food (fried food would need to be placed in just a enough water to cover and make wet/moist). Feed until symptoms disappear.
Introduction of Metronidazole to the aquarium water when feeding is OK.

Metronidazole can also be used in a fish bath. This is generally performed at double the "in tank" dose as per amount of water used in this bath. I recommend the use of Methylene Blue and maybe salt during this bath treatment too (once or twice per day for 7-10 days).
See: Fish Baths, Dips, Swabs

As with ANY treatment regimen, it is extremely important to follow correct procedures that includes addressing ALL water parameters and stressors (including oxidative stress.
Please read this easy to read article and follow ALL advice given as to proper treatment regimens:
Fish Diseases | How to Treat Sick Fish


*SeaChem Metronidazole, for Purchase
Recommended source to purchase based on extensive aquarium and pond professional experience dating back to 1978.
SeaChem's Metronidazole is the MOST PURE and easily used form of this antibiotic available to the fish keeping community

*API General Cure, for Purchase Contains Metronidazole & Praziquantel


Best Aquarium & Pond Medications
AAP Professional Aquarium & Pond Medications



Aquarium Medications 2; Antibiotics, Antimicrobials

*How Medications Work, and Which Ones to Use and Not to Use

Suggested other aquarium information resources & products:

AAP Spectrogram Fish Columnaris Treatment
AAP Spectrogram

THERE IS NO MORE EFFECTIVE treatment for Fish Columnaris!!

Fish Diseases, How to Treat Sick Fish
Fish Diseases | How to Treat Sick Fish

Aquarium Metronidazole, UV Sterilizer Use
Aquarium UV Sterilization; How UVC Sterilizers Work

Aquarium Medications, do not purchase at Amazon
Purchasing Aquarium & Pond Equipment via Amazon

YouTube & Facebook for Aquarium Keeping Information

Aquarium Metronidazole, SeaChem Products


Some of the best aquarium treatments available.

Wonder Shell
AAP Wonder Shells

The ONLY Authorized online seller of the full line of this unique product. Only FRESH product, not clearance product!!

Aquarium Metronidazole, Heaters

Aquarium Heaters; Submersible Quartz, Titanium

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Blogger Unknown said...

Can you still use the metronidazole powder to cure a bad bacteria infection in the body? If so how much do u use?

4:52 PM  
Blogger Unknown said...

Just completed a 7 day treatment of metronidazole for my guppies. I bought some wild guppies a year ago and they looked skinny so i figured it was worms. But now im pretty sure its Hole in the head, my question was (i also used prazipro) how long should i wait before using the medicated feed again?
I don't want to kill their liver, but some are still showing signs, especially the younger ones. Thinking about just culling the ones that look affected and waiting a couple weeks before treating with the med. food again, maybe trying the wonder shells too.

9:34 PM  
Blogger Unknown said...

Can this treatment be done on other healthy discus fish (through food) on assumption that they too are affected by the protozoans

4:48 AM  
Blogger Unknown said...

Can this treatment be done on other healthy discus fish (through food) on assumption that they too are affected by the protozoans

4:49 AM  
Blogger Unknown said...

This comment has been removed by the author.

4:14 PM  
Blogger Unknown said...

Metronidazole is effective against some B-lactamase producing bacteria that can cause disease in humans. Which type of anaerobic bacteria would be problematic in fish?

4:21 PM  
Blogger Unknown said...

Vanessa Cissna, 7 days is a minimum treatment time indicated by the author. Instructions for
treating with Metro for Hexamita typically suggest 7-10 days, and if you read National Fish Pharmacy instructions for their Metro, they indicate 10 days period, nothing less. Instructions vary and most instructions for treating with Metro indicate repeating dose every 24 hours with a 25% water change before treatment. Part of the reason for the water change is to help reduce the flagellites that are expelled in the feces into the water. A study at the University of Florida on Hexamita in Angelfish and treatment methods showed daily 25% water changes were almost as effective at reducing the amount of Hexamita in the intestines of affected fish as the metro. Here is the link from the study. In addition, for Hexamita, Metro should be combined with Nitrofuracin Green powder for 14 days to be truly effective. Metro for 10, Nitro in combination with the Metro but for 14 days. If you have not alread culled your guppies, there really is no need, you haven't really done an effective full treatment yet, only 7 days of Metro. Hope this additional information will help and allow you to keep all the guppies including the little ones.

6:15 PM  
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This is a life saving to my koi fish since I can buy it to drug stores

4:58 AM  
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Outstanding help an absolutely fast together with your get are suggested by Dr. Bruce Bateman

4:58 AM  
Blogger Eoin Morgan said...

How much is your budget for this aquarium? This might be obvious from someone on the outside, but it is easy to get caught up in spending hundreds of dollars in your first visit to the store. Successful Aquarium It is not uncommon to spend upwards of $1,000, especially for a reef aquarium.

8:12 AM  

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