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Common Fish Diseases and How to Treat Them

Common Fish Diseases and How to Treat Them

Written by: Tammy (@aquarist_tland Team Buce Plant



Just like people or any other living animal, fish get sick too! It’s common for aquarium fish to catch an illness when they’re stressed or living in poor conditions. Unfortunately, not many hobbyists see the signs of sickness until it’s too late. When you notice your fishy friends aren't doing so well, it can be a sinking feeling. You're left with the question: How do I treat my sick fish?

This article will go over how to prevent, identify, and treat these common fish diseases:

1. Ich / White Spot Disease

2. Fin / Tail Rot

3. Internal Parasites



Before we go into specific diseases and their treatments, let’s go over some prevention practices. Fish are most susceptible to sickness when they’re stressed. There are many steps you can take to keep their immune system up. It's important to avoid the poor tank conditions and poor water quality that negatively affect fish.

Remember, happy fish tend to be healthy fish. So, make sure your freshwater fish are kept in cycled aquariums and under proper water conditions for those specific species. For example, don’t keep tropical fish in cold water and vice versa. Make sure to always keep up on tank maintenance, including water changes, so the water stays clean and habitable.

Lastly, all new fish should go through a quarantine process. When you go out and purchase new fish for your aquarium, it is important to be mindful of the dangers that they might bring. Unfortunately, these new additions can introduce diseases and parasites into the tank. This is why it is important to always quarantine new additions to your fish tank.


Ich / White Spot Disease

fish ich

Ich, which is more formally known as Ichthyophthiriasis, is an external fish parasite that latches onto a their body, gills, and fins. These tiny creatures damage their host’s tissue when they feed off of it, which can lead to the death of the fish they’ve targeted by either direct damage or by secondary bacterial infections.

Once one of these parasites matures, it detaches itself from the host and falls to the bottom of the tank, where it multiplies to release up to 1,000 more Ich parasites into the water column. These newborns are free-swimming and ready to latch onto their next victims. This is why it’s essential that once you are able to detect Ich on one of your fish, you need to begin ich treatment ASAP. This disease will spread across to the aquarium’s other inhabitants fairly quickly.


Signs of Ich

●    Tiny white spots resembling grains of salt on a fish’s body, fins, or gills

●    Heavy and rapid breathing

●    Loss of appetite and energy

●    Agitation (trying to rub against objects or walls of the tank)


How to Treat It

Dips, or salt water dips, are a common way to take care of external parasites like Ich. Make a separate solution with 5-10 tablespoons of salt dissolved in 1 gallon of purified aquarium water before gently placing your fish into it for 5 minutes up to 30 minutes. Continue keeping an eye on your fish throughout this time. If they begin to swim erratically to appear distressed, immediately return them to their original aquarium!

In addition, you can treat Ich with medication. Luckily, since Ich is such a common disease there are many medicines available such as API Super Ick Cure and Aquarium Solutions Ich-X. Each medicine has their own respective instructions to follow, but here’s a general guide to you can use:

  1. Remove any activated carbon from the filter or aquarium.
  2. Add the proper dosage of Ich medication for your tank.
  3. Wait 24 hours (or however long the specific medication asks) and perform a ~ 25% water change by gravel vacuuming the bottom of the aquarium to remove as many Ich protozoans as possible. Once the water change is done, add the proper amount of medication again.
  4. Repeat step 3 until you don’t see any more Ich. The treatment may take a while as these parasites are only vulnerable to the medication in their free-swimming state.
  5. Replace activated carbon if you had to remove any from the aquarium.

If the Ich infestation was severe, a follow-up antibacterial treatment may be necessary to prevent any bacterial infections on possible open sores from tissue damage caused by the Ich.


Fin/Tail Rot

fin rot

Fin Rot is a common fish disease usually found in fish kept in poor water conditions or stressful environments. The edge of the infected fish’s fins/tail becomes ragged and begins to rot away. Usually, if it gets to the point where the disease reaches the base of the tail, the fish will die. Fin rot can be caused by either a bacterial or fungal infection.


Signs of Fin Rot

●    Edge of fins/tails become discolored or ragged/frayed

●    Segments of fins/tails have rotted away

●    Loss of appetite and energy


How to Treat It

Your first step to treating fin rot must be to remove the underlying issue that caused it in the first place. If it’s because of poor water conditions, clean the aquarium and perform a water change. It is essential to keep up on tank maintenance to prevent fin rot.

Check the pH and temperature of your tank water. Check that there is no chlorine, ammonia, or nitrite in the water, and the nitrate level is under 40 ppm. In addition, do not overfeed, feed outdated food, or overcrowd the tank as these can cause more stress for your fish that will lead to fin rot.

Since fin rot can have either bacterial or fungal origins, it is best to try and tackle both at the same time by using a combination of medicines. If you do this, please make sure that the combination of meds you use are safe to mix together. Examples for antibiotic treatments are API E. M. Erythromycin or Fritz Mardel Maracyn and examples of antifungal treatments are Methylene Blue, Aquarium Solutions Ich-X, and API Fungus Care.

Follow the instructions of whichever medication you decided to use until you see the disease has stopped progressing or if you notice the fins have started growing back.

  • TIP: Remember to remove any activated carbon from the tank or filter before using any medication. Carbon removes chemicals from your water and in turn will destroy the effectiveness of any medicine you use.


Internal Parasites

fish internal parasites

“Internal parasites” is a broader category to include diseases caused by worms or flukes that may live inside your fish. Examples of diseases caused by internal parasites are skinny/wasting disease and hole-in-the-head disease. These parasites leech nutrients from the fish they’re in, essentially causing the fish to grow weaker and weaker until it dies. The parasites can reproduce inside the host and spread to other inhabitants through the waste of the infected host.


Signs of Internal Parasites

●    Sunken belly or skinniness

●    Stringy white poop

●    Loss of appetite and energy

●    Swimming at surface and gasping for air


How to Treat It

  1. Remove any activated carbon from the filter.
  2. Use a medication that is effective against internal parasites such as API General Cure or Fritz Paracleanse. Follow the instructions and proper dosages for that specific medication. A full treatment usually lasts 5 days.
  3. Repeat a full treatment after 2 weeks. Fish with internal parasites should receive a second treatment because the medicine is not effective against the parasites’ eggs, so by 2 weeks the eggs should have hatched.



discus fish

If you notice any of your fish acting strange, I hope this article is able to help you identify whether the fish are sick or not and treat any possible illnesses they may have caught. Let’s all do our best to keep our fish happy and healthy!


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Trish Prather - January 20, 2022

We had a couple of large goldfish in a 20 gallon tank which was set up as a visual for my mother who suffers from Alzheimers. The gold fish grew rather large and we all have become attached to them. My partner decided to add some plants from the lake on our property (I cautioned agains this…) As I suspected, the gold fish have gotten a parasite. Your site helped me confirm this. It has been many years since I kept Discus and I could not remember exactly, but I knew that the swimming at the top of the water with semi clamped fins and gulping for air at the surface were all bad signs. I just wasn’t sure if it was a parasite or a bacterial problem. I will treat with Sachem Paraguard and see if this helps. Thanks so much for your informative and helpful website.

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