Molly Fish Diseases – How To Treat & Cure Them Properly

Molly fish are considered the go-to choice for aquarists thanks to their lovely appearances and low maintenance. However, like all animals, molly fish can still fall prey to ailments. Not only do such illnesses can negatively affect their lifespan, but they can also create problems for the whole tank.

If you wish to nurture a school of molly fish at home, make sure to read these guidelines on everything you need to know about molly fish diseases and how to treat them right.

Most Common Molly Fish Diseases And How To Treat

Swollen gills

Swollen gills are rather self-explanatory. This situation happens when the tank water’s quality goes down, affecting the fish’s ability to fight back carbonate and ammonia poisoning. Subsequently, your molly fish will swim around relentlessly, as they want to stay away from the water.

As swollen gills are directly linked to ammonia levels being left uncontrolled, the best thing you can do about them is to change the water. A 50% water change is recommended within the first few days since your fish starts developing the symptoms.

You are also advised to starve your fish since a fasting period helps to reduce the produced waste. Furthermore, spraying some nitrifying bacteria inside the aquarium helps to minimize the chances of infection.


Velvet is caused by a strand of parasites called Oodinium. Once it starts infecting, molly fish will develop the gold or yellowish cysts on their bodies. If left untreated for a long time, these cysts will tamper with the overall health of your fish and disturb the tank’s community.

If you spot these lesions, dose your fish with copper immediately. Copper is extremely effective when it comes to curing mollies of velvet. You can also hasten this process by dimming the lights, creating a more favorable environment for the fish to recover.

Usually, your fish take roughly a few days to become healthy again. After velvet has disappeared, replace 70 to 90% of your tank’s water.


Protozoan leads to a lack of energy, white spots on the body, extreme weakness, and lots of slimes. When your fish experiences scratch or open wounds, the protozoa will travel through the flesh and enter the bloodstream.

The best way to treat this disease is to regulate the temperature. If the water gets too hot or too cold, protozoan will spread out much quicker. Combine copper and formalin (or malachite green) treatment until your fish has fully recovered.

Then, perform a 70% water change to eliminate any lingering traces of protozoan.

Fin and tail rot

Fin and tail rot are demonstrated by unnaturally white strips across the bodies. Sometimes, the fin and tail also get stuck together, making it challenging for the fish to swim around. There is no definitive cause for fin and tail rot, but rather the accumulation of bacterial and fungal diseases.

When your fish are hurt and the water’s conditions deteriorate, fin and tail rot are sure to follow.

Treating fin and tail rot call for the removal of infected mollies. After placing them in a separate tank, dose the fish with the antibiotics prescribed. Before releasing the fish back into the original tank, make sure to replace 30 to 50% of the water.

This way, you can effectively prevent the reoccurrence of fin and tail rot.


Also known as ick, ich is associated with white spots scattered all over the length of a fish. In most cases, mollies will scrub their bodies against the glass walls in an attempt to relieve the discomfort.

The first step to minimize the disastrous impact of ich is to raise the temperature. Anything approximately 80 degrees Fahrenheit will suffice. Next up, ask experts about which medicine you should start dosing your fish with.

Adding a teaspoon of salt per gallon of water will help maintain the right conditions for your aquarium, thus making it easier for them to recover.

Red blood spot

A red blood spot happens when your fish starts having red stains on the body and stomach. When the levels of nitrate and ammonia spike, mollies will be subject to a high concentration of toxicity.

When it comes to red blood spots, a standard fasting period of roughly 24 hours and a 50% water change are the best solutions. At the same time, controlling the quality of your tank’s water is recommended to quicken this treatment process.

Molly Fish Disease Prevention Tips

While treating molly fish diseases are necessary, it is still better to take precautions beforehand. Below are some of the most useful suggestions you might want to consider.

  • Clean the decor: Rinse all of your decorative objects before putting them inside the tank. This helps to disinfect all the surfaces so bacteria and fungus cannot get in.
  • Keep the number of fish under control: If there are too many fish in too small a tank, chances are you will not be able to provide them with all of the necessary nutrition. Ensure that each fish has an average space of roughly 1 to 2 gallons.
  • Stock vital medicines: Most common molly fish diseases can be treated with prescribed medications. Check up with experienced aquarists and see what their medicine box includes.
  • Change the water frequently: Water changes are what keep a tank healthy and balanced. Should you leave your water in the same state for too long, the toxin levels will surely come up.
  • Monitor the relevant parameters: Keep an eye on the pH levels, kH levels, and temperature of your tank. Once any of these exceed the recommended limits, your molly fish are more likely to catch an illness.


Molly fish diseases are rampant, but it does not mean that there is nothing you can do about them. As long as you pinpoint these problems in the first place, getting rid of such ailments will be a piece of cake.