I've started seeing tiny white spots appear on one of my fish. After asking a friend, he told me it was something called "ich". What is ich and how do I get rid of it?


2 Answers 2


Ich Ichthyophthirius multifiliis

A white skirt tetra with Ich
(Source: aquariacentral.com)

Ich is an tiny ectoparasite that can harm fish if they succumb to it. If not cared for properly, it can kill fish.

It's important to note that ich is always present, and there is nothing you can do to get rid of it. Fish are naturally immune to ich, and only succumb to it when their immune systems or protective slime-coating have been compromised, or when they're stressed.

Think of it like a person with the flu. The flu virus will always be present, and our bodies have natural defenses in place to protect us, but external factors such as lack of sleep, a person who is already infected sneezing nearby, not washing hands, etc. can all cause the virus to get past our defenses and make us sick.

This is why you will commonly see fish contract ich after traveling, if they're being bullied by other fish, and when they're living in poor water conditions. Also, if you have a fish like a H. plecostomus (also known as pleco), loach, or certain catfishes, they will actually attach to other fish, and "bite" off their slime coating, exposing them to ich.

Finally, just like if you moved a person sick with the flu into a house full of healthy people, introducing a fish with ich into an established aquarium is a bad idea. And just like giving a healthy person flue medicine, giving healthy fish ich medicine isn't a good idea.

It's a good idea to have a small tank on hand, one that's big enough for one or two fish, so that you can quarantine and treat sick fish away from healthy ones.

For freshwater fish, ich can be treated in several different ways:

  1. Chemical treatment: something like Ich Attack or ParaGuard are two that I personally recommend. Follow the directions on the bottle, it'll tell you how much to put in per gallon, and how often. Be careful, these two shouldn't effect anything else in your tank, but with chemical treatments you always run the risk of throwing off the chemical balance (usually pH levels). Copper-based treatments like CopperSafe, while effective, are also really bad for invertebrates, like shrimp and crayfish. I would suggest avoiding copper if you have invertebrates in your tank.

  2. Aquarium salt: adding aquarium salt to the water helps calm fish, providing them with certain nutrients, and protects fish from nitrites via blocking gill absorption of nitrites, helping fish to absorb more oxygen. I wouldn't recommend using aquarium salt with H. plecostomus in the tank, as they can be sensitive to it, though some people have no problems. Also, aquarium salt is special; don't use other kinds of salt.

  3. Temperature: raising the temperature to about 86 degrees Fahrenheit (30 degrees Celsius) will create an environment that the fish can survive in, but not the parasite. Don't leave the temperature at that though, as it will stress the fish out to be in there for long. It's all about who can survive it longer.

  4. Aquarium salt and temperature: I prefer this option as the salt helps the fish through the temperature rise more. Again, think twice about salt and plecos.

For saltwater fish, the treatment is a bit more tricky. The first thing you want to consider is if your treatment will effect the live rock and any corals in your tank. In my opinion, for saltwater tanks, a small quarantine tank (with the same water parameters as the established tank) is a requirement. If you notice a sick fish, move it to the quarantine tank to protect the rest of your tank. There you can treat the fish without worrying about the medicine harming other fish or corals.

  1. In a quarantine tank, us chemical treatments on the fish. Since you're treating the fish in a quarantine tank, you can use copper-based treatments like CopperSafe. I have not had the guts to try it, but according to the bottle, Ich Attack is reef safe. Meaning you should be able to use it in a tank with corals in it without killing the corals. I'm not going to say you shouldn't do anything like that, but I don't want to take responsibility for anything like that.

  2. An UV sterilizer will help remove some of the parasites from the water. I've never used one, so I can't say much about them. They're expensive, and if you have the money for one, I think they'd be nice to have.

On top of the treatment, I would perform gentle water changes. Something like 10% every 5 days. Enough to take out a good chunk of the old water, but not enough to stress the fish anymore than necessary. Have a bucket of water prepared the day before with something like Seachem Prime for freshwater fish. For saltwater fish, use pre-mixed saltwater already heated to the right temperature to avoid any drastic changes.

  • For saltwater fish, a freshwater dip is an effective way to eliminate many parasites including ich.
    – Gary
    Commented Jan 2, 2015 at 6:17
  • "It's important to note that ich is always present, and there is nothing you can do to get rid of it." - This statement is false. It is a parasitic ciliate, without a host it will die between ~6-8 hours. It can only be killed in open water while traveling from a host back to the substrate to multiply. This is why it's key to begin treatment at the first sign of a single white spot. In my experience, if using heat treatment, the closer you can get to 90°F (permitting your fish) the better. Commented Jan 8, 2022 at 21:10

Spidercat outlined some good points, since the Ichthyophthirius multifiliis parasite is a very popular issue in aquariums i feel like adding my personal experiences as well.

Causes for an outbreak:

This can be but not limited to temperatures, pH and nitrite / nitrate levels, lighting, overpopulation! - environmental changes of all sorts. Anything that causes stress or weakens immune system of the fish.

Avoiding an outbreak:

AVOID STRESS AT ALL COST - when settling new fish, make sure the water temperature and pH levels don't cause a shock - it's highly suggested to measure tank temperature and pH levels and get information from the dealer about the water they use - otherwise measure on your own. If there are big differences use a second tank to bring the fish slowly to the level of your tank.

When settling in new fish I can't underline this enough, use a second tank for 2-4 weeks - specially if the new fish are weak, tiny, unhealthy, - in most cases the "new fish" will get the parasite first, this in most cases is not caused by the fish themselves but by a weakened immune system from the transport from the farm or a shock from the difference of water quality.

High nitrite and nitrate levels can harm the immune system of your fish and accelerate an outbreak.

Again, having a second tank with 30%-100% of the main tank water volume can be an immense help to either quarantine fish or to have "good water" at hand - so you can, if in need, settle fresh water over night and realize 90% water changes (I'll write about this below).

Let's have a look on the life-cycle of the Ichthyophthirius multifiliis parasite.

The white points / dots on the fish are the trophozoites - normally the first trophozoites are spotted on the fins. Once the parasite has gathered enough food he will release from the fish and enter the tomont (dividing) stage. The tomonts gravitate to the ground, but can stick to any ornamental object. The tomont divides up to 10 times - within 7 hours each tomont can divide in 1024 encapsuled theronts which attack the fish - from the the lifecycle repeats itself.

The parasite lifecycle is dependent on the temperature - wikipedia states that at 25°C / 77°F the lifecycle takes 7 days while at 6°C/43°F it takes 8 weeks.

The parasite does not like temperatures above 30°C and pH below 5,6 and above 9,2 - unfortunately, most fish cant stand that temperature and those pH values too - some fish can stand pH values below ~6 which also might be a help.

My fishes got the parasite, what can I do?

First and foremost, analyze the mistakes that lead to the spreading of the parasite - otherwise you will sooner or later face the same problem again.

There is no ultimate solution but a few points that certainly will, could help.

  1. If your fish can withstand it heat up the tank to 30°C - if not, proceed to 2.

  2. Make drastic water changes - 90% are reasonable (Here is why a second tank with prepared water can be helpful - you can resettle the fish every day in the prepared water or just change the water of the tank. AGAIN MAKE SURE THE FISH DON'T HAVE TOO MUCH STRESS.

  3. Get vitamins and Artemia - your fish need to stay strong.

  4. If possible separate the infected fish from the healthy fish (again a second or 3rd tank for this purpose is helpful.

  5. Get an UV-C clearer - in this case bigger / more is better - got multiple filters, put it on each filter, maybe even get one intern UV-C clearer - the more water you can clear from the parasite per hour the better.

  6. AVOID STRESS at all cost - if the tank is in a frequented room put a towel on it.

  7. I did manage to clean fish from the parasite by grinding along wit ha finger (only works if you are really careful, otherwise you do more bad than good)

  8. Clean all plant and other inventory during the sterilization process multiple times.

  9. Clean the gravel during the sterilization process with a gravel cleaner - best to do this before the daily 90% water change - same for the plants and other inventory.

  10. Diatom or sand filter (I haven't tested this yet).


  12. Medication.

Final words:

If there is an outbreak clearly something went wrong. Tanks are a biological environment where every change can put it out of balance.

Fish dealers are not always experts, often they are great salesmen. It's a huge commodity to have a fish dealer who loves aquaristics and is not just doing his job as salesman.

I have been doing aquaristics for 22 years, the best advice I got was online and from books in 90% of times. Reading about water and fish will prevent such problems as ichthyo.

Last but not least, aquaristics is a serious hobby which needs dedication, passion and some financial efforts to have a long lasting positive experience - the reward if those are put in is awesome - I love my hobby :).

  • I recently was asked to help with itchyton on a aquarium with a swarm of neon tetra. I could successfully cure ~ 30 neon tetra out of a swarm of 44 without medication with uv light, daylight only, heavy water changes and grinding every parasite from the fish carefully using my finger and the dip net. The separation was 4 weeks with the above measures. Water had ph 6.3-5. Teh aquarium was below a big window with all sides darkened in a unfrequented room. I used 1 intern and 1 extern filter with mechanical daily replaced "wool", the aquarium was 80 litre 90% filled.
    – Aurigae
    Commented Nov 11, 2016 at 10:41
  • Additionall info: Sol del mar (must be pure without iodine or other additions) in a dose of aprox 5g per 250 litre of water can help a wounded fish to build up his mucosal - this can be particular helpful for wounded fish - however, use with care because the salt also dehydrates the fish. To help a fish heal wounds, also useful for fungus infections.
    – Aurigae
    Commented Aug 4, 2018 at 1:54
  • the UV-C clearer has been reported as a very effective prevention solution - highly suggested.
    – Aurigae
    Commented Jun 2, 2020 at 14:30

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