Saltwater ich treatment: A comprehensive guide

A lot has been written about saltwater ich treatment, one of the most important and most common challenges in the saltwater aquarium hobby.

Articles on the topic, including those I’ve written in the past, are often littered with cliches like: an ounce of prevention is worth a pound of cure, because once the parasite gets in your tank, it is extremely difficult to get rid of.

The traditional advice is to quarantine all of your new arrivals for 28-30 healthy, symptom-free days before adding them to your display tank, to prevent the transfer of this parasite into your display.

But the traditional advice will not keep your tank safe!

While this advice serves as a good start and is arguably more than what most people do, I wanted to dive deeper into the science and determine how sound this advice truly is.

The rationale for this often-cited time frame (28-30 days) is that the entire lifespan of a saltwater ich parasite begins and ends in that 28 day period. This means that parasite is born, finds a host (parasite infects your fish), reproduces and dies all within that time frame, starting the circle of life all over again.

Most quarantine or treatment protocols advise treatment and observation for a similar period of time in order to declare, the coast is clear.

The theory goes that if you can avoid affecting any fish (eg. leave your fish in quarantine, under treatment for that period of time), you can add them to your tank relatively risk-free.

I am not an expert in infectious fish diseases, (although if I am ever invited to a cocktail party, I may pretend to be one, because it sounds impressive), but I did a fair amount of research to:

  • Determine what we truly know about saltwater ich
  • See what scientific evidence was there to support the commonly held beliefs
  • De-mystify what we know about saltwater ich

Saltwater Ich Lifecycle

As mentioned a bit earlier, the saltwater ich lifecycle (the time and stages it takes to hatch/emerge from a cyst, infect a fish and create more infectious copies of itself), has traditionally been listed as about 28 days.

What I found during my research is that the saltwater ich lifecycle tends to be about 21 days, but variability and survivability are the key. Much of what I capture here was learned by reading Colorni 1985 as well as other sources.

What are the stages of the saltwater ich lifecycle? Trophont, protomont, tomont, theront.

saltwater ich lifecycle


The trophont stage of the lifecycle is the stage most people intuitively think of when they think about saltwater ich, because this is the visible stage where you see your fish infected. While in the trophont stage, the saltwater ich parasite is embedded within the basal skin layer on your fish and is covered by a white capsule. These white capsules are the characteristic white spots you see when you fish is infected


After gorging on the flesh of your fish for about 3 to 7 days, the trophonts detach from the fish and begin to fall to the bottom of the tank. The protomont phase of the lifecycle describes the period where the parasite leaves the fish to settle on the bottom but has not fully formed a cyst yet.


The tomont stage of the saltwater ich lifecycle is where the parasite forms a hard, protective cysts. The cyst will stick to rocks, sand or the aquarium glass. Within 1-2 days, the saltwater ich tomont will begin to make hundreds of copies of itself, called tomites. These tomites will emerge from the cyst, once matured and will eventually be the free-swimming stage, called theronts, that will re-infect your fish. In case you missed that not so subtle point a few lines back, but a single tomont will create hundreds of free-swimming, infectious parasites.

It is important to note that when an organism forms a cyst, it does so for protection. Yes, this cyst stage is the reproductive stage, where the parasite makes copies of itself. It is also the stage that can tolerate and survive extreme conditions and wait out any rough periods until there is a more conducive opportunity to emerge.

The tomont is, perhaps, the most resistant stage to saltwater ich treatment.


The theronts emerge from the tomont cyst after about 7-12 days. At this point, the theronts eat their way out of the shell and swim around the tank looking for a free meal. Generally speaking they will swim around for about 2 days. If they don’t find a host in that period of time, most of the marine ich theronts will die.

If they do find a host (a fish) within that time, it takes them less than 5 minutes to eat their way all the way to the basal skin layer and embed themselves in the flesh of your fish.


This is also the stage of the lifecycle that is most vulnerable to saltwater ich treatment.

A note on surviving

Based on the outline just provided, it seems that the typical or expected lifecycle of a happy, healthy, infectious and actively replicating population of saltwater ich should turn over in about 3 weeks. However, a very important addition to this notion is that not every saltwater ich parasite is going to live for 3 weeks.

The same way every single human isn’t going to live to be 79 years of age, every single saltwater ich parasite isn’t going to live for the average age. Some will die earlier, some will die later. In humans, living longer is generally seen as a good thing…but when you’re a parasite, the longer you live (or remain dormant), the longer you remain able to infect fish and cause an outbreak in the tank. As was mentioned earlier, since each Tomont has the ability to produce hundreds of clones, it only takes one reproducing parasite to cause problems in your tank.

How long can a single ‘batch’ of saltwater ich last in your tank? In two different studies, it was shown that saltwater ich can survive in your tank as a cyst (Tomont stage) for 72 days and 5 months, respectively.

A single “batch” of saltwater ich has been shown to survive as long as 5 months in captivity waiting to reproduce

I’ve traditionally kept my fish in a quarantine tank for 28 days, that is clearly not enough.

A Guide to Saltwater Ich Treatment

The good news is that there are several different ways to treat a saltwater ich/marine ich infestation. The bad news is that all of those saltwater ich treatment methods require you to remove your fish from the display tank and treat them separately from any invertebrates, because the stuff that kills saltwater ich will also kill the invertebrates in your tank, including shrimp, crabs, clams, anemones and corals.

Here are a few of the most popular methods for saltwater ich treatment:

  • Copper
  • Formalin
  • Chloroquine
  • Hyposalinity
  • Transfer method

Using copper (copper sulfate) as a saltwater ich treatment

Using copper to treat a saltwater ich infection is probably the gold standard method. This is the go-to method that is often described in articles about the topic. According to Noga 1996, the therapeutic dose of copper sulfate is 0.15-.20 mg/L of Cu2+.
It is recommended that you take 2-3 days to reach the therapeutic level, to avoid any unintended toxicity towards the animals you are trying to treat and protect (de Boeck 2003).

Once you achieve the therapeutic dose of copper (0.15-0.20 mg/L), maintain the copper concentration at that level by testing twice a day and adding more copper to maintain the therapeutic level for 3-6 weeks, minimum (Noga 1996).

Copper is notoriously unstable in saltwater

Copper is notoriously unstable in saltwater (an unfortunate characteristic for the ‘gold standard saltwater ich treatment’), which is why it is recommended that you test your copper levels in the morning and the evening with a high quality test kit. There is a formulation of copper treatment that is more stable in saltwater, called chelated copper (Coppersafe is one tradename), but according to Noga 1996, this type of copper, while more stable in saltwater, is a less effective saltwater ich treatment.

Using formalin and hyposalinity to treat saltwater ich

Formalin is an effective agent in treating saltwater ich, especially when combined with hyposalinity. According to Francis-Floyd and Petty 2009, the recommended dosing regimen is 16 ppt hyposalinity and 25 mg/L formalin. You will need to dose 25 mg/L formalin every other day for 4 weeks.

Using chloroquine to treat saltwater ich

Chloroquine is a relatively newer chemical treatment for saltwater ich. The therapeutic dose is 15 mg/L. Unlike some of the other treatments (like copper) which are unstable in saltwater, chloroquine remains active in your saltwater until you remove it with water changes or activated carbon, which makes it a unique marine ich treatment.

The downside of using chloroquine as a saltwater ich treatment is that there are no commercially available tests to help you monitor the levels of chloroquine in your saltwater. You measure once, add it to your tank and hope you got it right.

Using hyposalinity to treat saltwater ich

Hyposalinity is one of the most popular ways to treat saltwater ich—because it doesn’t involve any tricky chemicals and because it can be monitored with the same equipment you already have — a hydrometer or refractometer.

I found two separate published methodologies for using hyposalinity to treat saltwater ich:

  • A pulsing method
  • A constant method

Pulsing method

The pulsing method of saltwater ich treatment was published by Colorni, in 1987. He recommends diluting the water in your quarantine/hospital tank by 5% every hour down to 10% seawater strength.

Once you reach 10% strength, hold the salinity there for 3 hours and then reverse it back 5% per hour until you return to full strength seawater.
Repeat this process every three days (dropping to hyposalinity for 3 hours on day 1, 4, 7, 10).

Constant method

In 1996, Noga published a somewhat easier hyposalinity methodology which became a bit more popular and mainstream than the pulsing method. Dr. Noga recommends you reduce salinity from 35 ppt by 5-10 ppt, per day, until you reach a level of 15 ppt salinity. This should take you about 2-4 days.
Once you reach the intended therapeutic level, 15 ppt, he recommends you keep the salinity at that level, by replacing water lost to evaporation, for 21-30 days.

Using the transfer method to treat saltwater ich

The transfer method is perhaps one of the oldest and still remains one of the best ways to treat saltwater ich.

The basic premise with the transfer method is that you move the infected fish to a clean, disinfected tank every few days. After the move, you clean and dry the old tank, removing any cysts and after a few more days, move the fish back to the first tank. When you do this, the parasites that fall off the fish never get a chance to reproduce and reattach to the fish, so after a few cycles of this, once all the parasites fall off and get removed, the fish have been cured.

In 1987, Colorni wrote about this. If you want to use his method of saltwater ich treatment, simply transfer your fish to a clean tank on days 1, 4, 7 and 10, cleaning and drying the alternate tank for at least 24 hours in between uses.

The reason I consider this to still be one of the oldest and best methods for saltwater ich treatment is that even if your fish are infected with a persistent strain of the parasite, like the parasites in the studies that survived as a cyst for 72 days and 5 months, respectively, the saltwater ich will all be removed and either cleaned out or killed during the 24 hour dry period. This mitigates the advantages that even the most persistent strains would have.

Free Downloadable Reference Chart

If you want to keep these methods in safe place under your aquarium to refer to later on, here is a link to a free download.

saltwater ich treatment spreadsheet image

Saltwater ich treatment: combining methods to achieve greatest chance of success

Recently, in Coral magazine, there was an article by Szcebak that highlighted the method used at Roger Williams University. They essentially use copper along with a freshwater dip and the transfer method, in order to be extremely certain they are not introducing parasites into their tanks there. Using different, complementary methods to eliminate parasites makes a lot of sense if you want to control the risks of contamination. The formalin method highlighted here (Francis-Floyd 1996) also combines use of the chemical formalin with hyposalinity.

What to do if your display tank becomes infested with saltwater ich?
The best way to deal with a saltwater ich outbreak is to prevent one from happening, in the first place. The best way to prevent a saltwater ich outbreak from happening is to quarantine new arrivals and use the transfer method to ensure no parasites get in your tank.

If your fish become infected with saltwater ich inside your display tank, here is what you should do:

  • Remove all fish to quarantine/hospital tank and treat
  • Leave display tank fallow for >5 months to wait out any rogue tomonts
  • Consider increasing the temperature a couple of degrees, if you can do this safely, to speed up the saltwater ich lifecycle and increase your chances of eliminating the parasite
  • Consider adding biological and UV controls on re-entry (if you didn’t wait the 5 months)

a comprehensive guide to saltwater ich treatment


My recent research into what has been published about saltwater ich treatment has expanded my understanding of this tenacious parasite and its ability to survive in our tanks, despite our best efforts. As a result, I’ve shifted my own beliefs away from thinking…28 days of hyposalinity…alone…is enough. It’s not. The research data suggests it is not. Do yourself a favor and figure out an easy way to employ the transfer method and even consider combining methods, like the crew at Roger Williams University does.

For more information

For more information, I recommend you check out these resources:


  1. Great article! Very insightful. I have not read about the transfer method and it makes a lot of sense. To do this method, would the filters also have to be swabbed out too? If you do a combo of copper treatment and the transfer method you cannot use carbon in your filters to treat the ich. What is the suggestion for managing the filters for your quarantine tanks?

  2. Hi,

    I am about to set up my first saltwater tank for the first time. So should I have a quarantine tank and keep my fish and corals in this for 28 days before putting them in my display tank?

  3. Author

    Hi Bryan, thanks for the comment and great question. You need to prevent moving things from the one tank to the next. Everything you use should be dry for at least a full 24 hour period before moving it on to the next tank. So for your specific question about filter, you need to have a separate filter and not mix.

  4. Author

    Hi Stephen, yes you should absolutely quarantine your fish. I’d even recommend using the transfer method while in quarantine. If you don’t, then 28 days of consecutive parasite-free days is the bare minimum for quarantine–and if you want to take some of the research cited here to the full extent of what they say–even then you bare some risk that your fish still has a chance of transferring the saltwater ich. It’s not all that practical to keep the fish in QT for 5 months…which is why I’m now going to be doing the transfer method while I wait in QT. Hope that helps.

  5. Hi,

    What is your take on using Paraguard as a safety precaution when adding newly purchased fish to the QT tank? Good idea or bad?

  6. Author

    Hi Paula, thanks for the question. Paraguard is an aldehyde-based medication. If you used it to either dip or treat prior to quarantine, it would theoretically lower your chances of adding parasites to QT that are currently on the outer surfaces of your fish. So, from that perspective, it’s a good idea. It’s also known to be a relatively gentle medication. The downside would be the expense and subjecting your fishes to another medication (if they didn’t need it). In my estimation, there is no one right or wrong answer. Quarantine is about how much time, energy and cost you can (and want to) afford to put into prevention. If you’re willing and able to put Paraguard in as a safety precaution, that’s a good step and then use the other methods listed here for treatment if you detect anything.

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