Ich: What is it & what to do about it?

Key Symptom: White spots that resemble large grains of salt on the entire body and fins (NOT cotton-like tufts, a whitish film or a white mouth/tail)

“Ich” is one of the most well-known aquarium “diseases” but is often misdiagnosed or used as a catch-all term for unrelated conditions. So, what is it actually? “Ich” is a shortened nickname for a freshwater parasite, Ichthyophthirius multifiliis. There is a very similar saltwater parasite with similar symptoms, Cryptocaryon irritans (not to be confused with Marine Velvet caused by Amyloodinium parasites which will be discussed separately). For our purposes here, we will be referring to both Ichthyophthirius multifiliis and Cryptocaryon irritans as Ich since they behave and are treated essentially the same.

What is it?
Ich is a type of parasite known as a protozoan. They live externally on fish on the scales and can occassionally be found on the gills as well. The parasite itself is too small to be seen with the naked eye but is shaped like an egg when viewed under a microscope. The white spots associated with Ich are actually the cysts the parasite produces during one stage of its reproduction. Ich has three life stages - trophont (visible stage), tomont (after the adult parasite drops off of the host), and thermont (free-swimming stage searching for a host). The entire life cycle can last up to about 3 weeks depending on water chemistry. Only the thermont stage is vulnerable to most medications so it is important to use all medications and treatments as directed to target the vulnerable life cycles effectively.

Where does it come from?
Contrary to popular belief, Ich is not “always present” in an aquarium but fish weakened by transport, temperature changes, poor water chemistry or another condition are more vulnerable to outbreaks. Ich cannot live without a host so a tank without any fish can generally be considered Ich-free after about 2-3 weeks.


- Higher Temperature
Raising the temperature in the aquarium a few degrees (not higher than 80-82 degrees Fahrenheit for most aquariums) will speed up the life cycle of the parasite past the medication-resistant phases to make the medications more effective.

- Dietary Supplements
Dietary supplements containing garlic are thought to help boost the immune system of most fish and increase their ability to fight off the parasite on their own.

- Copper Treatments
Copper treatments are effective against most protozoan parasites but aren’t safe with invertebrates, some types of fish or live plants. Concentrations must be maintained within a specific range for at least 3 weeks to treat effectively. Always follow the instructions carefully.

- Malachite Green/Methylene Blue
Medications with these two active ingredients are usually effective Ich treatments. Both are blue-green dyes and may be combined with other active ingredients like Formalin (a formaldehyde compound) in parasite treatments. These medications CANNOT be used in combination with copper and may stain some surfaces. Always follow the instructions carefully.

Similar Diseases/Conditions

- Oodinium/Amblyoodinium (SW)
Also known as “Marine Velvet”, Oodinium and Amblyoodinium are also saltwater parasite but is caused by a dinoflagellate rather than a protozoan. Instead of granule- like spots, Marine Velvet looks like a patchy, misty covering.

- Brooklynella (SW)
Brooklynella is another saltwater protozoan that mostly affects clownfish. It especially attacks the gills, causing heavy breathing in the fish as well as loss of color, loss of appetite, overall lethargy and an increase in the slime coat. It also has a mistier look on the body than the Ich parasites.

- Lymph (SW)
Lymphocystis is a virus that affects saltwater fish. It usually shows up on the edges of fins but could appear on the body as well. It looks like cauliflower-like tufts.

- Fin Rot/Columnaris (FW)
Also known as Mouth Rot or Tail Rot, this condition is caused by a bacterial infection that attacks the fins or mouth and moves towards the body. It is usually accompanied by a fungal infection that gives the area a fuzzy look. The gram-negative Columnaris bacteria and poor water quality or sudden water quality changes are responsible for most cases of Fin Rot.

- Bacterial Infections (FW and SW)
General bacterial infections are usually caused by a wound or injury, or poor water conditions like high Ammonia or low pH. It may looks like a rough white coating, red patches or red sores. The edges of sores may be white and fuzzy (see below).

- Fungal Infections (FW and SW)
Fungal infections are usually a secondary condition that appears because the fish is already weakened by another problem. It looks like tufts of cotton and can appear anywhere on the fish, particularly around an existing wound.

Tips to avoiding Ich (and other parasites)

• Use a quarantine tank and monitor new arrivals before adding to your main tank.
• Monitor water quality regularly since poor quality will weaken fish.
• Feed a high quality and varied diet to promote healthy immune systems.
• Never add water from a new fish’s bag into your tank.
• Avoid exposing the tank to drafts, low temperatures or temperature swings.