Curing Fish of Marine Ich

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Well-known member
May 22, 2006
Curing Fish of Marine Ich :evil:


There are several posts and threads in this Forum which describes the disease, choices for the cure, and the process to cure marine fishes of Marine Ich (Cryptocaryon irritans). It seems like a lot to read and it can get confusing. So here’s a “short” procedure to follow that refers to those posts that have all the details you’ll need.

Much of what is written is assuming the hobbyist has found that one or more fish in the display system is displaying this parasite. Thus much of the instructions below are based on this assumption. If you discovered the newly acquired fish of yours that you put into quarantine is infected, so much the better. There will be much less work. Just ignore those parts that assume the display tank is infected, and the fish being treated is coming from the display system.

I'm writing this in blunt, easy to read English (I hope). It may sound 'stern' but I am being blunt, short, to the point AND I'm sure what it is you need to do. :)


Before you start, you want to be as sure as you can be that you are dealing with Marine Ich. If you’re experienced, you probably know and can skip this part. If you are new to the hobby or have never come across this parasite before, you’ll want to search the Internet for photos of fish that are displaying this parasite.

Unfortunately, most of those photos you will find are of fishes with an advanced case of the disease, having many dozens to hundreds of spots. At the outset, your fish may only have a couple to a few. But those photos should give you an idea of what to look for. Marine Ich has many stages in its life cycle. The one we humans can see with our unaided eye is when the parasite is ready to leave the fish. The spot is white and about the size of a grain of salt or sugar. It can be found on fin or body of the fish. When severely infecting the gills (the parasite isn't seen, but. . .), the fish will flash (scratch) and/or breath rapidly (more than 100 swallows per minute).

So do the diagnostic step first.

Know Thy Enemy

I don’t care if you’re experienced or not, you must sort out the myths from the facts about this parasite. READ this: Marine Ich - Myths and Facts The better you know and understand what it is you’re dealing with, the better you will be at the cure and stopping future infections.

This part includes understanding that not only the fish you see with spots have been infected, but ALL THE FISH in the display system are infected and must be cured at the same time.

Decision on Cure

You need to get a grip with reality. There are no short cuts, miracle cures, use of garlic, or any one of a dozen other 'secret chemicals' you can buy that cures, 100% of the time, marine fish of this parasite. The cures presented do not require prescriptions, and work 100% of the time when performed diligently. Give it up!

[Read this paragraph if you don’t believe the above]. The aquaculture industry loses millions of Dollars a year to this parasite. Don’t you think that if there was a short cut, miracle cure, that it would be on the front page of every aquaculture and marine aquarium hobbyist periodical? Of course it would be. But. . .There aren’t any front page headlines. We’ve know about this parasite for more than 200 years. It’s been studied. Not much more to learn about it. There are many chemicals that adversely affect the parasite and even though a bottle may contain those ingredients, it doesn’t happen to cure the fish or kill them all. Read what those bottles say closely. Read the fine and bold print. Do they claim to always kill all the parasites or to totally cure the fish? No. That’s because there are only a handful of ways to do this and their product isn’t one of them. There are just three sure ways that are cheap for the hobbyist to cure marine fish of this parasite. Two of those ways are easy, one is hard. So the two easy ones have prevailed. Others exist which require prescription drugs, and drugs that are cancer causing drugs in humans. Not a good idea to go this route, even if you can/could get hold of the drug(s). I mean, we’re talking a hobby here, not saving a human life.

You need to decide on the cure. There are two basic ones guaranteed to cure your fish (when performed properly): a copper treatment or a hyposalinity treatment. DON’T ask which one to use. Either works. Decide on which one you are most comfortable doing. Read about each cure so you can understand what each requires you to do. Choose the one you can handle best. In order to decide, read these two posts:
Copper Medications - Good, Bad, and Ugly
A Fish Hyposalinity Treatment

As additional guidance, choose the Cupramine (copper) treatment when there are sign of a severe condition (more than 30 spots on a 3" fish at one time), when the fish has a secondary bacterial infection (the antibiotic Maracyn Two for Freshwater or Saltwater fishes can be used at the same time Cupramine is used), or when the hobbyist cannot spare the time for a hypo treatment.

No Shortcuts

Buy the things you need to do the cure. The quarantine tank(s), the medication and the test kit (for copper), the refractometer (for hyposalinity), etc. DON’T come up with your own procedure. The procedure has worked for more than the 40 years it’s been used. Don’t try to improve upon it or take any shortcuts. It is as short and as simple as it can be.

Start The Quarantine Tank(s) (QT)

Read about setting a QT up and do it. In this case it is technically a 'hospital tank' but the tank is setup the same as a QT. If you have a lot of fish to treat, then you can choose a large QT or multiple smaller QTs. Your decision again. To begin with, you can use display tank water in the QT. Both it and the fish are ‘infected’ so it doesn’t matter. AFTER that though, all water changes will be done with new salt water. Read this: A Quarantine Procedure

Starting Out

Hopefully, you found that the fish you purchased and have in quarantine was infected with Marine Ich, instead of having put the fish into your display and now your entire display is infected. If the disease is in the display, then this is what to do: Move all fish (those with and those without spots) to a quarantine tank (or multiple QTs) and begin their cure. (NOTE: During the move DON'T do any freshwater dip unless the infection is REALLY bad -- hundreds of spots and/or the fish is breathing so fast; and/or the fish flashes every minute. If you read up on the enemy you'll know that a fresh water dip NEVER cures fish of Marine Ich -- BUT it can help a little in extreme cases.)

If you need help in how to catch your fish, keep in mind two things: These fishes (unless tank bred) were caught by people in a whole ocean or sea (and all you need to do is catch them in a small box) and; you're smarter than a fish (I hope :D ). In addition this thread gives you some ideas on how to go about doing this: Catching Fish

The Display System (and Tank)

If the parasite was in the display system, then leave the display tank and the entire display system go fishless for no less than 8 weeks. Some people don’t seem to understand what this means. This means you can leave every other living thing in the display system, except fish. Please don’t ask if it’s okay to leave ....?... in the tank. If it isn’t a fish, then it’s okay to leave it in the display system! For this purpose, Eels, Mandarins, Gobies, Sharks, etc. are all fish. :)

Some people want to take this opportunity to put into the display system additional clean up crew, corals, invertebrates of any kind, etc. It’s okay to do this, but the 8-week clock begins AFTER the last addition. Keep in mind this is only for Marine Ich. If you don’t routinely quarantine new marine life forms, you might be bringing any other kinds of fish diseases into the aquarium. BUT, with the 8-week fishless time, there won’t be any Marine Ich alive.

Sometimes it’s just better to tell the hobbyist DON’T add anything to the display system during this time. This is good advice.

What to do with the display system while it's going fishless: Keep feeding all other marine life. Add food to keep bacteria alive and working. Keep lights on as usual. Keep water quality up and continue with the usual maintenance. Keep water temperature at the high end of the range (about 78 to 80F). Keep all equipment going. Keep testing water for quality and maintain, maintain, maintain. This is a very good time to do substrate, rock, and decoration cleaning.

Additional Pointers on the Quarantine Tank

NO BIO FILTER GOING? If the QT doesn’t have an active and working biological filter, you can AND MUST still do either cure. You will need to setup for a biological filter (see post on setting up the QT) and you will do water changes every time you detect ammonia and/or nitrites in the water, until the biological filter takes over. Waiting for the biological filter to start to begin treatment is very wrong. :mad: The fish(es) is sick. Get going on the cure. (NOTE: If you will actually READ the reference QT post, it gives some ideas on the use of chemical filters to help reduce ammonia and nitrites).

You will need to buy ammonia and nitrite test kits (not test strips) and test the water two or three times a day until the biological filter is fully functional. Four if you feed often. You will need to remove all excess food and fish wastes. This you can do by siphon or by one of those sand cleaning pumps (manual) to pick up and filter out the debris.

NOTE: Even if you have an active and operating biological filter, still check the water for ammonia and nitrites. The fish might just be polluting too much and the filter has to catch up. So even with a biological filter running, CHECK the water daily for ammonia and nitrite and make a large water change if either or both are detected.

When you detect ammonia and/or nitrite you’ll need to do a large (over 80%) water change with new water. Since this will be a large water change, this post tells you the proper way of doing this: How to Make a Successful Water Change

You will need to control the water quality very well in the QT so the fish don’t ‘know’ any reduction in water quality during their cure. One part of that is pH. If you chose the hyposalinity treatment, it is easiest on the fish, but hardest on the hobbyist as is stated in that post. Controlling the pH will be a challenge since the water is so ‘thin’ that the chemicals/salts (buffering ability) aren’t there to stabilize the pH.

Many recommend feeding the fish less during the cure so the water won’t be as polluted. I don’t go along with this approach. The fish needs good nutrition during this time – better than ever – not going on a diet or a reduction of food. The hobbyist has to compensate by doing more work on keeping the water quality high. Keep feeding the fish the best foods with vitamin and fat supplements in it. See this for nutritional info:Fish Health Through Proper Nutrition

All this extra effort of making large water changes when ammonia and/or nitrites are there could be reduced if the hobbyist had a biological filter running in the display system or display sump as suggested in the quarantine linked post. The active biological filter would be ready to go into a QT with display tank water and everything moves forward easier. But not having a biological filter is NO REASON to not start the treatment. With or without an active biological filter, the procedure is to move quickly to the treatment.

NOW FOR SOMETHING COMPLETELY DIFFERENT. . .Some hobbyist don't understand this part about the QT. Since there is no skimmer and no carbon running, the water still gets polluted even when no ammonia or nitrites are detected. Because of this, even if the biological filter is running properly and no ammonia and no nitrites are detected, the hobbyist must still make a large water change every two or three days (depending on how many fish you are treating) to keep down high concentrations of organics, nitrates, and other pollutants. DO THIS.

VERIFY the Fish are Cured

Don’t mess up now! After the treatment (either one you choose) remove the copper or return the water to normal salinity as instructed in the linked post. IN ADDITION, after the water is returned to normal salt water, hold the fish in the QT for no less than 4 more weeks in normal salt water to SEE if the fish are cured. If any sign of Marine Ich shows itself first be sure you have the correct diagnosis. If it is Marine Ich, do not despair – the QT was contaminated somewhere along the line or there was a slip up in the treatment (wrong copper concentration, wrong sp. gr. etc.). Fortunately the fish aren’t back in the display so you can perform another (more careful) treatment.

The End Game

Fish are verified to be cured (see above). Display system has been fishless for no less than 8 weeks (if the parasite was in the display system). Time for the cured fish to go home. If there were many fish, put one fish back in weekly until all are in. If the fish are small (under 1") put more in at one time. If fish are large, put in one at a time in two week intervals.

Hopefully (as noted earlier) the fish was newly acquired and you quarantined it, so the main display wasn’t contaminated. Thus, being one fish, it is ready to go into the main display system.

You’re Done

Don’t let the parasite into your display system. Use the quarantine process to prevent Marine Ich from getting into your display system.

Last edited:


Active member
Nov 2, 2008
good article, especially the part about continuing to do the water changes during the eight week interval.
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