Although some diseases are extremely contagious and can attack healthy guppies even in well-maintained tanks, the vast majority of diseased guppies are the result of stress. The most common cause of guppy stress is poor water conditions or a sudden change in tank water parameters (such as pH bounce). Once disease is firmly established in a tank it is usually impossible to stop. The fish in the photo below is an example of a very unhappy fish, he’s sick.
- If one or more of your fish become diseased, check the chemistry of the water, including ammonia and nitrite levels. Remove diseased fish. Resist the natural impulse to feed sick fish, as uneaten food quickly adds toxins to the water. If the water tests zero for ammonia and nitrite then it’s usually a pathogen.
- Make daily partial (30%) water changes to bring down the level of bacteria or toxins in the water. Doing larger water changes will stress the fish.
- Do not resort to medications for a quick fix. We have found only a handful of medications actually eradicate disease. Most bacterial or virus medications disturb the biological cycle, creating stressful conditions just when the fish are least able to tolerate it. Medications formulated to kill internal parasites and some external parasites have a higher success rate. It is very important to follow recommended dosage levels and treatment programs. Overdosing will stress or kill the fish. Under dosing ensures the survival of medication-resistant pathogens.
- If you have no idea what pathogen is affecting your fish, use Potassium Permanganate to kill most external pathogens (except such large parasites as lernea and very small bacterial or fungal diseases). PP also reduces the organic load in the tank, creating more favorable conditions for recovery.
- Diseased store bought fish are common. Very few fish stores have the knowledge or desire to maintain proper water conditions for guppies, and the guppies they buy wholesale often arrive at the store severely stressed. Disease may take several days or weeks to appear. Even guppies acquired from friends or a dealer may have diseases your fish are not immune to. An isolation tank is de rigueur (what did I say?). How about ‘required by etiquette or proper’.
- To disinfect a tank that has housed sick guppies, fill it with water and one cup of bleach for each nine gallons of water. Let it sit for half an hour. Empty it and let it air dry. Be careful of stronger or longer dosage regimes. Bleach can eat away at tank sealants. Quarantining new fish and maintaining optimum water conditions and good feeding practices are the best disease fighting tools at your disposal. For more detailed information go to ‘Diseases and Treatments’ article.