Saltwater Ich

Saltwater Ich

Saltwater Ich

Saltwater ich—the war in your aquarium and how to stop it

I was surfing the old world wide web for interesting content and found a very scientific article about treating saltwater ich, written by Steven Pro. I have included a link to it at the bottom of this post–I encourage you to check it out–it is a very informative (almost academic) piece.

Something Steven wrote in that article really inspired me as a jumping off point for this piece that I’m writing. Here is a quote:

“Many hobbyists are fooled into believing they have cured their fish of the parasites, only to find Ich present again on fish a few weeks later; a reason why following through with a full treatment protocol is so important. Don’t make this mistake and be lulled into a false sense of security. The parasites may be in a stage where they are merely regrouping and multiplying for their “next offensive.”

Steven’s use of the phrase “next offensive” set off alarm bells in my head. Dealing with saltwater ich is a battle–a war that is waged in stages–and the only way to win the war is to understand what the enemy wants, how it will attack, and where it is vulnerable.

With a polite nod to Steven for his inspiration (he wrote that piece in 2003; I’m a bit late to the party), here is a look at saltwater ich, the war it wages in your saltwater tank, and how you can defeat it. I will shine a light on this little parasite’s motives and reveal its militaristic plan for total aquarium domination.

What does saltwater ich want?

Not unlike many militaristic expansions in human history—saltwater ich wages war in your aquarium to exploit resources (in this case, the fish and environment in your saltwater tank) and expand. Now that we know what your enemy wants with your aquarium, let’s dig into how it plans to wage this war.

How does saltwater ich plan on dominating your aquarium?

  • Step 1: Get inside (infiltrate) your tank
  • Step 2: Bring in the clones (saltwater ich clones)
  • Step 3: Release the ninjas (free-swimming Cryptocaryon parasites)
  • Step 4: Repeat steps 1-3 until there are enough parasites to win
  • Step 5: Dominate the tank

Step 1: Get inside (infiltrate) your tank

The first step in saltwater ich’s plan for aquarium domination is to get inside your tank. The most common way it will infiltrate your tank is by hitchhiking into your tank on the gills or skin of a fish you just purchased. You may not know this, but saltwater ich may already be in your tank. (LOOK BEHIND YOU!!!)

Step 2: Bring in the clones (saltwater ich clones) 

saltwater ich clones itself

Once inside your tank, saltwater ich plans to hide-out until it is time to strike. Under the cover of darkness (really, there are data that demonstrate this happens at night–check out the Steven Pro article linked to at the end of this piece), while your fish are asleep (do fish sleep?), the parasite will:

  • Release itself from the skin and gills of the fish that brought it into the tank
  • Drop to the bottom of the tank
  • Encase itself inside of a protective cyst
  • Make a clone army

That last bullet bears repeating…the saltwater ich makes an army of clones inside the cyst while it lays on the bottom of the aquarium waiting for the right time to attack.

Step 3: Release the ninjas (free-swimming Cryptocaryon parasites)

saltwater ich ninja armyOnce the clone army is built inside of the cyst, saltwater ich waits for the cover of darkness again to launch the next phase of its attack. While your fish are haplessly resting at the bottom of the tank, he saltwater ich clones emerge from the cyst, like an army of ninjas and attack. At this stage, Cryptocaryon iritans is free-swimming and the parasites move about to find a resting fish to attack.

Step 4: Repeat steps 1-3 until there are enough parasites to win

The parasites gorge on your fish until they drop to the bottom of your tank, make another clone army of ninjas and start all over again. Each and every little nija parasite can create hundreds of clones of itself.

Step 5: Dominate the tank

If each parasite could consistently produce 200 clones of itself, one tiny hitchhiker Cryptocaryon parasite can turn into 8,000,000 in just 3 generations. If left untreated, a saltwater ich infection could become so intense that it overwhelms and kills your fish. It happens to aquarists all the time.

Because the population of ich in your tank has the potential to grow exponentially (like a virus), timely treatment is important so that you don’t get an overwhelming infestation. Don’t dismay, despite the impressive plans that saltwater ich has for your tank, there is a weakness–and that weakness creates an opportunity for a counter-attack.

What is saltwater ich’s weakness?

Cryptocaryon has two main ways to protect itself:

  • While it parasitizing your fish, ich will try to bore deep inside the skin or gill tissue of your fish, to limit contact with the outside world. Entombed by the living tissue of your fish, the parasite will be difficult to attack
  • When it drops to the bottom of your tank to create the clone army of ninja parasites, saltwater ich will encase itself in a protective cyst–making it harder to kill than a cockroach.

The only time saltwater ich is really vulnerable is when the ninja clone army emerges from the cyst to attack your fish. If you can hold-off the clones for 24 hours, preventing them from finding a host (attacking your fish), they will die.

How do you Treat saltwater ich?

fighting saltwater ich

The three most popular ways to treat saltwater ich and defeat the ninjas are:

  1. Prevent the infestation—while technically not a cure for saltwater ich, the best thing you can do is keep the war OUT of your tank. Develop, and rigorously follow a proper quarantine protocol to keep saltwater ich out of your tank.
  2. Kill free-swimming parasites with copper—copper is perhaps the most common medication and treatment for saltwater ich—but copper treatments should not be administered without careful testing. At the proper therapeutic dose, copper does a fantastic job killing saltwater ich and almost any other invertebrate in your tank. You should NEVER (I’m not yelling, but did you notice the bold font and capital letters?) dose copper in a reef tank, or any tank that you want to house invertebrates in the future. Even in non-reef tanks, copper can be lethal to your fish too, if the dose is too high. At too low a dose, copper will not cure your ich problem. And as if that wasn’t tricky enough, copper is unstable in saltwater and doesn’t last very long–so you have to test regularly and add back enough copper to keep the dose at the appropriate level.
  3. Kill free-swimming and exposed parasites with hyposalinity—while the word may impress your friends while playing SCRABBLE, it’s not that complex of a concept. The prefix hypo means ‘low’ and salinity refers to the amount of salt in the water. Treating your fish with hyposalinity therefore just means lowering the salt content of your water. Saltwater ich may seem like a survival machine, finely tuned to dominate your aquarium after impressive specialization and evolution, but it cannot survive in a hyposaline (low salt) environment. The process of treating saltwater ich with hyposalinity basically involves replacing the saltwater in your quarantine tank with pH-adjusted freshwater until you reach a specific gravity of about 1.009-1.010. At this salinity level, your fish will be fine, but the parasite will not. The biggest challenge hyposalinity poses for the saltwater aquarist is knowing how long to keep the fish in hyposaline conditions. The Steven Pro article points to a reference that demonstrated ich was killed in 14 days, whereas another article on suggests 1-3 months may be necessary. Personally, I have had success treating with hyposalnity for about 5 parasite-free weeks.

How Long Do You Have to Treat Saltwater Ich?

how long to wait

As I mentioned above, saltwater ich is really only vulnerable to treatment during the free-swimming phase, when the parasite clones emerge from the cyst to find their next host. So on the surface, it seems like you should only need to treat the aquarium for a day or two to kill all of these little ninjas. The problem with that logic is that it assumes each and every little parasite was on the same schedule/timeline–when in reality, each parasite could possibly be working under its own biological clock. Because of this, most recommendations for treating saltwater ich try to account for enough time for straggler parasites to release to the bottom of the tank, encyst and release the free-swimming clones. Sometimes cysts can also lay dormant at the bottom of the tank, so the best advice I can give is to make sure you maintain your treatment of choice at therapeutic levels for long enough to kill even the stragglers–because one lonely parasite can become 8 million in a matter of months.


I hope you enjoyed this article, and perhaps have an appreciation for why proper quarantine and treatment are so important in the saltwater aquarium hobby. One thing I didn’t really get into was how difficult it is to get ich OUT OF your aquarium once it gets in. But for some reason, we aquarists (myself included) seem to be hard-wired to be impatient, impulsive creatures. I’ve battled with saltwater ich a few times–and it took a devastating, overwhelming infestation for me to really understand the importance of quarantine and set up my own system. My hope is that I’ve laid this out in a way that causes you to take action and help prevent injury to the amazing fish in your tank–but if you don’t, I totally understand. I was the same way. Just tuck this article away and read it when you, or someone you know needs it.

I attempted to keep things informative but also light-hearted. If you really want to educate yourself, I can’t recommend Steven Pro’s article on Marine Ich/Cryptocaryon iritans enough.

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Written by Albert B. Ulrich III. Follow me on  and Twitter


  1. Hi,
    Very interesting article on the pesty ich problem, which I have in my tank right now, I had been Vodka dosing to lower nitrates which seems to have worked, the problem I have now is that my quarantine tank isn’t big enough for my 8 fish, would it be safe to lower salinity in my main tank ? I have tried using API Pimafix to help my fish fight any flesh problems caused by ich, but I have noticed several turbos have died, not sure if that is because of Vodka dosing or the Pimafix, any suggestions would be gratefully welcomed.

  2. Author


    Thanks for the note. Sorry to hear you have ich right now. that sticks. Remind me, Alf, do you have any invertebrates in your tank? If so, you have to remove them before doing hypo salinity. I sent you a private email to try and help.

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