How to treat saltwater ich

Saltwater Ich, also known as Marine White Spot Disease, is caused by the parasite Cryptocaryon irritans. The term “Ich” is a generic carry-over from the freshwater parasite Ichthyophthiriius. Since both parasites cause white spots on the fish, the disease is universally called Ich, even though they are different parasites. A saltwater ich outbreak in a marine or reef aquarium is a serious matter. In aquariums and aquaculture environments, fish loss due to an ick outbreak can be very high. Let’s take a closer look at this parasite and learn how to avoid it and if necessary, treat a marine ich outbreak.


What Does Saltwater Ich Look Like?

The cryptocaryon parasites are microscopic, which means you can’t really see them with the naked eye. As aquarists, what we notice first are the symptoms of the parasitic infestation on our saltwater fish, which typically includes: ragged fins, scratching behavior (the fish scratching itself erratically) on rocks or sand, and of course the hallmark white spots or nodules on the gills, fins and body of the fish.

saltwater ich

saltwater ich on a yellow tang. Wikimedia creative commons

But just because you don’t see white spots on a fish’s fins or body doesn’t mean that the fish is not infested with saltwater ich. Sometimes the ich parasites infest primarily in the gills, showing no white spots or other outward symptoms, so it might be worth trusting your gut instincts if you are pretty sure the fish is sick, based on your observation of their behavior.

If you just aren’t sure, you may want to try doing an internet search for images of saltwater tank to get a feel for how it looks when different species of fish are infested–here is an interesting link for that:

 Marine White Spot Disease: Know Your Enemy!

Before entering a battle, it is important to know who or what you are up against. It is the same way with fish diseases. In order to understand how you have to fight marine ich, it is helpful to take a moment to understand the life cycle of ich.

Saltwater ich has a complex multi-step life cycle.

  1. The feeding or trophont stage is where the parasites are swimming around under the skin and gills of the fish. The parasites eat cells and fluids, damaging tissues and leaving the fish in a weakened state. Here is where you may see the white spots and other outward symptoms. Ich treatments generally do not affect the trophonts because they are protected under the skin of the fish.
  2. Once the Trophonts are fattened up, they leave the fish as a protomont.
  3. Protomonts lose their ability to swim, fall to the bottom of the tank and in a few hours becomes a tomont. The parasite becomes a hardened cyst, like an ich egg, waiting to hatch. The tomont is a ticking time bomb full of nasty little parasites. What was once a single ich parasite, now divides again and again, storing up hundreds of new parasites called tomites.
  4. After a number of days or even weeks, the cyst opens up and the infective parasites are released as free-swimming theronts, seeking to attack your fish. This is really the primary stage that ich medications are effective against the parasites. The thereonts have about six hours to find a fish and burrow into the skin, becoming a trophont. Then the cycle begins again. Depending on the severity of the outbreak, an aquarium or shop full of marine fish can be wiped out due to the reoccurring nature of the parasite life cycle.
saltwater ich life cycle

saltwater ich life cycle (Calorni and Burgess)

Preventing and Treating Marine White Spot Disease

The best way to protect your saltwater fish tank or reef aquarium is prevention. Prevention means keeping ich-infested fish out of the aquarium. This is done with a quarantine tank. The idea behind quarantine is to isolate a new fish, observe it for several weeks, ideally one month to make sure the fish is healthy. A quarantine aquarium can be as simple as a ten or twenty-gallon tank with a heater and filter. If the fish is carrying a hidden ich infestation it will likely show up during quarantine. If it does, your quarantine tank helps you keep from infesting your main aquarium and also provides you with a small, safe location to treat your sick fish.

There are several ways to treat ich in a quarantine aquarium.

The water change method to treat saltwater ich

One method involves making 50% water changes every day for two weeks, paying careful attention to being able to siphon off anything lying at the bottom of the tank. Which means you must have a bare bottom tank if you have any hope that this is going to work. If you remember back to the third step in the lifecycle (listed above), the protomonts fall to the bottom of the aquarium and become tomonts. The idea here is that since you are vacuuming up the bottom of the tank, each and every day, you should (in theory) be able to remove all of the tomonts/cysts before they become problems. Of course, since a single parasite can explode into many copies of itself in a short period of time, this method certainly does have an Achilles heel. If you miss even a few, you may not eradicate the problem.

Hyposalinity to treat saltwater ich

Another non-chemical treatment for saltwater ich is called hyposalinity. One of the forces of chemistry that every aquatic creature must face is called osmotic pressure. Osmotic pressure is the principle behind reverse osmosis water purification in your RO/DI filter (if you have one). You can employ osmosis to your advantage to destroy saltwater ich by lowering the salinity of the water to a level that is close to freshwater (close, but not quite). Please note that you should only do this with hardy marine fish species, not with any invertebrates at all.

The hyposalinity method is fairly straightforward. Gradually lower the specific gravity of your aquarium water to 1.009-1.010 or so and keep it there for a few weeks. Monitor your fish for signs of increased stress caused by the change in salinity and stop/reverse the hyposalinity treatment if the fish is under extreme stress. But in many cases, you should be able to lower the salinity without much difficulty.

Once you feel fairly certain you have eradicated all of the ich parasites, slowly increase the salinity to the normal range over a few days to get the fish acclimated to full strength seawater, before placing it in your main aquarium.

Freshwater dip

The freshwater dip is an old yet effective method against a variety of parasites, including saltwater ich. It is actually a more extreme spin-off of the hyposalinity method. The goal of the freshwater dip is to put the infected fish in complete freshwater for a short period of time (2-5 minutes) to kill off any of the parasites on the outside of the fish.

Fill a bucket with dechlorinated tap water, RO or deionized water. Use a heater to match the temperature to the aquarium. Use a pH buffer to bring the pH to match the aquarium. Be sure to add an air stone to oxygenate the water. Now add the fish to the bucket for two to five minutes. Some fish show no reaction while others sink to the bottom.  There is no reason to panic, this is normal. If you are observing extreme stress, it is probably best to return the infested fish to a quarantine tank and treat the infestation a different way, but if your fish handles the treatment reasonably well, you may be able to kill off enough of the parasite for this method to work.  Some aquarists have found wrasses and firefish to be sensitive to freshwater dips. Use caution and watch the fish and don’t push your luck if your instincts are telling you the fish is not holding up.

Commercial treatments

Two popular commercial treatments for saltwater ich are copper (cupramine) and formalin. These treatments can be challenging because they are toxic to both ich and your sick fish—so you have to be very diligent about following the manufacturer instructions and making sure you do not over-dose the fish. Under-medicating the aquarium carries the separate risk that you won’t even cure the infestation. So medication can be a bit tricky.

The magic cure for saltwater ich

Haha, that was a dirty trick, for me to use a headline like that, but I regret to inform you that there is no magic cure for saltwater ich. So don’t believe the hype, especially if the product claims to be completely reef safe, organic, recycled, or has other slick marketing (and this is coming from a marketer).

I don’t want to bash any products here, but if you have any doubt, I encourage you to try and find out from others in the hobby if the miracle elixirs work. Make sure you ask enough people to get a few data points.

Am I missing anything? How have you treated saltwater ich in your aquarium?


  1. Thanks for the very interesting material, one question, would I have to remove my corals if I try the lowering of salt salinity.

  2. Author

    Hi Alf,

    Thank you for leaving a comment/question–great question. It is almost impossible to treat an aquarium containing corals for a saltwater ich plague. That is one of the biggest problems with the whole situation. Any of the treatments (including lowering the salinity) will kill your corals. So the only way to treat the ich infestation, once you have it, is to remove all the fish to a separate tank and treat them in that separate (hospital or quarantine) tank. That’s the tank you lower the salinity in–not your display tank with corals.

  3. Many thanks for your reply, I asked the question because I over heard an employee where I buy my fish and corals, tell someone to lower their salinity in their tank, it seemed a strange comment to make, so I’m glad I asked you the question, I’m now in the process of setting up a hospital tank, thanks again for your reply.

  4. Author

    Alf, I’m very glad you asked that question, too. Kudos on setting up the hospital tank. Please feel free to ask-away.


  5. Can sand Gobies get white spot ? If yes, is it safe to give them the fresh water treatment ?

  6. Author

    Alf, thanks for the question. I’ve never kept the sand goby, but if it is the species linked to here, it is a brackish water species which suggests it would do better than average with freshwater (hyposalinity) treatment. I think all fish are susceptible to white spot (ich), although some have greater barriers due to immunity or scales, etc., I would not expect this fish to be particularly resistant to it. I can say that I’ve kept neon gobies and they seem extremely prone to white spot (which seems ironic to me). I do wonder/hypothesize that a sand goby kept in brackish water may be less likely to encounter fit white spot, ich, parasites–but I don’t have data to back that up. hope that helps. If it is a fish, I would tend to be cautious and quarantine first, assuming they may be prone to get or transmit white spot.

  7. Hi, sorry I should have said a Watchman Goby in my salt water tank, not fresh or brackish water, just to recap, do they catch white spot ?
    Also, is it safe to put treated marine fish straight from a hospital tank to the main tank ?

  8. Hi Albert B Ulrich III
    My name is Akbar. I have some experiences to fight to Cryptocaryon irritans with Chloro quine phosphate & also Chloro quine Sulfate.
    Both of them are very successful. Specially when you use it with H.S. together. I also have good experiences with hypo salinity process. The only thing that you should care of it, when you chose hypo salinity, is bacterial problems. At least, it was for me so. I think that by hypo salinity, bacterial problem appears more than in salty water. What do you thing about this hypotheses?

  9. Author

    Akbar, I have used hypo a few times and have not had (noticed) problems with bacteria. However, I can relate one human phenomenon I’ve observed that may be related to your hypothesis. Forgive the tangent here–but I know when we gave our kids antibiotics, to fight bacterial infections, we had to watch out for thrush, which was a viral infection…essentially clearing the bacteria made the children more prone to a viral infection that otherwise wouldn’t have competed with the bacteria. Similarly, we see issues with diatoms and cyanobacteria in early tanks but then not as much in established tanks…I suspect if we were to use medicine to selectively peel back those layers, you might see a similar situation where cyano or diatoms would take back over.

    Perhaps, and I say a big perhaps, that could also apply here–if hyposalinity depletes the parasites…perhaps it leaves the wounds more prone to bacterial infection than they would have otherwise…also, infected fish are likely weaker than an average fish and therefore probably more prone to ‘catching something else’ before they recover. So your hypothesis seems reasonable to me. It isn’t what I observed, but I have not observed enough to be anywhere near definitive, I think you have identified an area that would be a great research project. Makes me wish I worked in a fish lab. In terms of advice for anyone reading this, I’d just caution that this is a hypothesis/discussion, I’m not sure whether or not bacterial problems are in fact more likely, but those are my initial thoughts in response to your question. thanks so much for the intriguing question.

  10. My goby has itch. He’s in quarantine. I’ll never not have a QT again. I hope my other fish aren’t infected. I just got him and noticed the spots. Anyhow, I’m using the tank transfer method. All of his spots dropped off so I got him out immediately and into a new tank. If he is still infected will new spots appear?

    I can tell he doesn’t feel good. Now I know why he was hiding under the frags at the LSF. He doesn’t like the light since he is sick. I have the light off of him here at home.

    Thanks, kelly

  11. Author

    Kelly, thanks for the question and sorry to hear about your sick fish. As the theory goes with the tank transfer method, if you keep moving the fish, you break the life cycle of the ich and the fish will eventually be parasite free.

    Unfortunately, I learned about the importance of quarantine the same way you did…I dealt with the hassles of infection and then decided not to let it happen again. Good luck. Please take some notes about your journey here and let us know how it goes. Hoping to hear more about how often you moved the fish and what you observed

  12. Hi Al,

    How do I get him to eat? He hasn’t eaten since I’ve had him. A full week. I’ve tried soaking mysis with garlic to entice him, brine shrimp, bloodworms, and flake food. He’s not interested. Please advise and thanks.

  13. I have found the best food for my Goby is Vitals Algae Pellets, I turn all howerheads and pumps off and get some pellets in my fingers below the top of the water, and rub them between my fingers so that rather than float on the surface they sink right down in front of the rocks where he is hiding behind, once the pellets have settle I turn just the pump on so the smell of the pellets starts to drift around and eventually the Goby comes out to eat some , he’s very temperamental, some times he will come out within minutes, sometimes he might not show up for half an hour, so I don’t put too many pellets out in one go, mind you the other tanks inhabitants will usually eat them up.

  14. Thank you Al. I went and dropped tiny algae tablets in the tank for him after I turned off the filter. I then turned it back on, and he came zipping out which really surprised me then snubbed them. Hopefully he will change his mind.

    By the way, he is pooping really long white stuff. Is that okay? Thank you again.

  15. Umm, sorry, that I can’t answer as mine hides beneath the rocks and only come out to feed, however, they do sift through the sand, so if your sand is white, that may possibly explain it.

  16. Author

    Kelly, do you have access to any live foods? That often helps stimulate picky eaters to eat. Can you hatch some baby brine shrimp? If not, do you have any ways to make your prepared foods look more…alive by putting them in the current or changing the way they appear. Also, could you confirm what type of goby? I know we discussed previously, I just can’t remember?

  17. Hi there,

    She’s a neon goby. I have copepods and amphipods. She’s not interested. However, I think she ate most of the algae pellets last night. All that was left were a few that moved behind her fake anemone. I’m hoping they didn’t get sucked up into the filter. I was going to start brine shrimp and see if that would stimulate her. I don’t want her to die. This morning, she was asleep under a little decorative bridge I put in for the tank so she could hide. She seems to be staying stressed; heavy breathing. How long can she keep that up? She is getting plenty of oxygen. Thanks for coming up with some more ideas. You are the best!

  18. Author

    Hi Kelly, unfortunately, the rapid breathing isn’t a good sign. I think of them as behaving ‘high strung’ naturally, so easy to spook, they move in rapid, darting, movements–so everything is fast–but if the breaking is abnormally fast that might not be a great sign. If she’s eating pellets, that’s a good sign! Brine shrimp are like potato chips for fish…hope that one works. Fingers crossed. Sorry for forgetting she was a neon. I don’t know why I thought you might have also had a yellow watchman. I may just be losing it ;).

    What about other things to make her less stressed…can you dim or darken the lights a bit, see if that helps? not total darkness, just take the intensity down a bit.

  19. I have a moonlight on for her. Is there something I can give her to pull her out of shock?

    I’m crossing my fingers she ate those pellets. She’s been breathing fast for over a week now. No need to apologize for forgetting she is a neon. I lost the neon I named Baby. He just never gained weight. I have two watchman gobies. They are so funny to watch. I have one in each tank.

  20. Hi Kelly,
    Have you checked your nitrate levels ? I have a similar situation with my watchman Goby, heavy breathing not coming out to feed etc. etc. I found my nitrate had jumped up, so I had to put him in a hospital tank while I treated the main tank, after a week and a half everything was back to normal and I was able to put him back in the main tank again, he is now back to full health

  21. All water parameters are perfect. I change 50% of the water in her tiny tank daily anyway. Good news, she is moving about now. Looking interested at things. Not hiding. I’m keeping my fingers crossed.

    Thank you so much for your ideas and thoughts. Please keep them coming cause you never know. You may just hit the nail on the head.

  22. Good news. My neon goby is still in Q; however, she is feeling so much better. She is quite perky. She is pigging out on brine shrimp. she has three more weeks to stay in QT.

  23. hi . i want to know that if i am keeping my tank fallow ( fish free ),… and without any corals or invertebrates , how do i maintain my live rocks and beneficial bacteria in my sump filter , any guidelines for that ? or just leave the tank as it is.. and what about lighting time and all

  24. Author

    Hi Agneesh, sorry to hear about your ich challenges. You leave the corals in the tank, just remove the fish. Feed your corals as you would normally, leave the lights on for them as normal as well. Your filter and live rock will be fine. Then just add the fish back slowly once they’re cured (so as to not overwhelm the filter on the return)–that’s my advice. What do you think?

  25. I have a 125 gallon with many fish and corals so a quarintine would be out of the question, what are my options to treat the ICH? get rid of the sand? what about the corals and rock? how do I treat the entire tank? You said 50% water change every 2 days, that seems incredibly expensive , just the ro alone. Raising the temp? its a real mess and if all the fish die what do I do then? leave the tank for 2 months? Is Kick ICH any good?

  26. I have a 125 gallon with many fish and corals so a quarintine would be out of the question, what are my options to treat the ICH? get rid of the sand? what about the corals and rock? how do I treat the entire tank? You said 50% water change every 2 days, that seems incredibly expensive , just the ro alone. Raising the temp? its a real mess and if all the fish die what do I do then? leave the tank for 2 months? Is Kick ICH any good?

  27. By the way, Just finished the 31 day tank and now I have ICK, Bummer

  28. Author


    Your only good option here is to remove the fish to a quarantine tank where you will treat the ich to get rid of it. All the while, you leave your tank fallow (empty of fish) where the parasites will die out without a host (takes a very long time). You can leave the corals in. Turning up the temperature (just a few degrees to the high end of the appropriate range) speeds up the lifecycle of the ich, which means it will die out sooner. You don’t go extreme with the temperature.To your point, you want the remaining inverts to be healthy.

    Sorry about the ich. that stinks

  29. Our tank got ICK and all the fish died. All that we have left is a crab and 2 fat shrimp. We completely reset the tank. Since all the fish were dead and we wanted to switch from a canister filter to a sub-pump we decided to go for it. The tank is up and running smoothly now with only the crab & shrimp. We kept the live rock and the live sand from the previous tank. If we let the tank sit without adding new fish will the ICK eventually die off? If so, how long should we let it sit? I’m really antsy to get more fish in the tank but I’m very nervous to lose $700 in fish again.

  30. Author


    Thanks for the great question. I’m sorry to hear that your tank got ice and your fishes died. There are studies that have shown that saltwater rich can survive in your tank for as long as 5 months. That’s not ‘typical’, but it is certainly possible and has been shown in an experiment.So the real answer is that you should wait that long to be absolutely sure. Conventional advice would suggest you need to wait a month at the bare minimum, since most of the parasite should be dead in a month. It’s up to you and your risk tolerance to decide how long you want to wait to be sure the coast is clear. Will you be able to set up a quarantine tank? You can start acclimating new fish to quarantine so you’ll be ready when your tank is.

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