Aquarium Fish Diseases

How to Treat Ich in Aquarium Fish

It’s never fun to discover a sick fish in your aquarium, but what can you do if you have an outbreak of infectious ich? White spot disease is one of the most common afflictions in freshwater tanks, and most aquarists will experience at least one major outbreak. What causes white spots on fish? Can fish recover from ich?

Guide to treating ich disease in fish

Working in an aquarium shop in college, I was approached almost every day by customers looking for solutions to their aquatic problems. One of the most common complaints was white spots on tropical fish or goldfish. I always thought white spot disease was aptly called “ich or ick” because it really is a gross and complicated problem.

What is white spot disease?

While there are several things that can cause fuzzy white spots or patches on aquarium fish, the most common cause is the dreaded white spot disease, or ich. What is ich and how long does it take to go away?

Signs and symptoms of Ich

Ich is a disease caused by an infectious parasite. How do you know if your fish has ich? It’s not always obvious to the naked eye, and several other infections can mimic white spot disease in the early stages. Your fish most likely have ich if they exhibit the following symptoms:

  • Small white spots or dots that appear at night on the gills, gill covers, body, head, or fins.
  • Scratch or rub against the substrate or aquarium decoration.
  • Loss of appetite and/or lethargy (moderate).
  • Holding the fins against the body (advanced).
  • Gasping for air near the surface of the tank (advanced).
  • Bloody rashes or ulcers on the body, head, or fins (advanced).

Ich is a progressive disease that usually comes on suddenly and continues to spread. To add to the challenge, not all diseased fish exhibit the distinctive white spots. With mild infections, they may just have parasites hiding in their gills where they can’t be seen. You may not notice the subtle signs until other fish get sick.

White Spot Disease: Cause and Prevention

What causes the ick? The responsible parasite is a protozoan known as Ichthyophthirius multifiliis, which literally means “The fish louse with many children”. It is found in freshwater bodies throughout the world and is a scourge to wild and farm-raised fish as well. Let’s take a detailed look at the ich life cycle.

Ich parasite life cycle

The protozoan goes through 3 distinct stages of development. Here are some important facts you need to know before diving into the details of your reproductive cycle:

  • It is more difficult to treat the infection in the early stage, when the protozoan attaches to the fish and becomes encapsulated in their skin.
  • If you disrupt your free-swimming stages, you may be able to stop an infection in its tracks.
  • This cycle is also temperature dependent; at 86°F, the parasite completes the cycle in about 5 to 7 days, while at 50°F it can take 3 to 4 weeks.
Stage 1: the parasitic trophon develops into white spots on the body

When a fish becomes infected with ich, the parasitic trophon becomes encapsulated in the epithelium, or top layer of skin. This is what causes the slightly raised white spots on your infected fish. . The trophont feeds on the tissues of the fish and causes irritation around the edges of the capsule.

Stage 2: reproductive development of Tomont and Tomocyst

When the trophont reaches the ideal size, the cyst breaks open and the free-swimming tomon emerges into the tank. The tomont eventually attaches itself to the tank, substrate, decorations, or plants and becomes surrounded by a protective gelatinous cyst. This tomocyst is where they reproduce.

Within the tomocyst, mitotic cell divisions take place and produce the next generation of daughter cells called tomites. Up to 1,000 tomites can be produced from a single tomocyst, and when they reach maturity they break through the cyst wall.

Stage 3: Infectious Theront completes the cycle

When mature theronts emerge, they swim through the water in search of a suitable host. They can quickly infect any fish in the tank. Theronts can survive for several days in water, but if they don’t find a host to attach to, they can’t continue reproducing and the cycle is broken.

How to prevent white spot outbreaks

There is some debate as to whether ich is always present in aquarium water, but without a doubt, stress and poor water quality make it much more likely that your fish will get sick. If your fish has a hidden infection, it may not show signs until its immune system collapses from stress.

Ich prevention tips for fish tanks:

  • Keep up with your water changes and filter maintenance and make sure the conditions in your tank don’t change quickly.
  • Unstable water parameters can stress your fish, so use a heater to maintain a consistent temperature and make sure you don’t overfeed or feed erratically.
  • Quarantine new live fish and plants. in a separate tank for 7 to 14 days (or longer for cold water species) and never place new animals or plants directly into your community aquarium.
  • Remove diseased fish at the first sign of illness and keep them in a hospital tank for treatment.
  • Use a UV sterilizer on your tank.

Treatment of white spot disease

Can fish recover from white spot disease? Ich is a delicate disease and some fish do not survive the infection. It depends on how quickly you notice the problem and how much damage the protozoan causes. However, if a fish does survive, there is a very good chance that they will have at least partial immunity to further infection.

Ich treatment is also problematic, because the drugs cause stress and are themselves highly toxic. An infected fish can develop secondary infections from the ulcers and also require antibiotics. Let’s take a quick look at the methods used to control white spot disease in aquariums.

Malachite Green, Copper Sulfate, and Other Medications for Ich

It was once common to treat ich by dosing a tank for 7 to 14 days with a toxic mix of chemicals like malachite green, copper sulfate, or other parasitic drugs like formaldehyde, and some aquarists still use these treatments. These medications do not penetrate the skin of the fish, but should be targeted at the free-swimming stage.

If you choose to treat the entire tank, you will need to remove the chemical and biological filter media and perform daily 25% water changes. Be sure to vacuum the gravel to get as many of the stage 2 and 3 parasites as possible. Alternatively, if you only have one or two fish with symptoms, you can use a hospital tank to treat them individually.

use aquarium salt

Another method that has had some success is the use of non-iodized aquarium salt to increase the salinity of the water. This can help relieve the itching caused by the cysts on your fish and will hopefully kill any free-swimming parasites. You will want to remove any filter media and do daily water changes as you treat your fish.

You will need to research the ideal salinity for your tank based on the type of animals you have. Some fish are much more sensitive to saltwater than others and may not be able to handle the ideal dosage. You will want to maintain salinity for at least 7 to 14 days.

Natural treatment methods: temperature and tank changes

Since medication and salinity treatments can be stressful and even fatal to some fish and certainly many live plants, some aquarists choose to control an outbreak through safer and more labor-intensive efforts.

Increasing the temperature of your tank can speed up the ich life cycle in a predictable way, and it is recommended that you gradually raise it as high as your fish can tolerate, even if you are treating the tank with salt or medication. However, you will want to add an air stone to increase the oxygen in the water, as warmer water holds less of it.

Along with rising temperatures and daily water changes, some aquarists also rotate their fish to a new tank every 5 to 7 days until the infection has cleared up. That way, free-swimming stage 3 protozoa cannot find a new host and perpetuate the infection. You may lose some sick fish, but save the rest of the tank.


Ich is a common but complicated problem in freshwater aquariums, and it is much easier to prevent than to treat. Unfortunately many treatments cause more stress and not all fish can survive the infection. However, by using the information in this guide, you can reduce mortality in your tank and prevent the problem from coming back.

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