How to Clean a Tank After Ich Killed All Your Fish?

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Whether you’ve heard of Ich before or not, now’s the time for a more in-depth dive into the subject. Ich is a fairly common parasite that most fish will face at some point. Despite being relatively easy to combat and eliminate, Ich has quite a high mortality rate.

This may seem paradoxical, but there is an explanation for that. The answer is that many people fail to recognize and treat the condition in time.

This allows the parasite to spread fast and infect other fish before you even realize it’s there.

If conditions allow it, Ich will kill your entire fish population fast. The only thing left now is resetting your tank. So, let’s get into that.

Cleaning Your Tank After Ich Killed All Fish

It’s not that common for an Ich infestation to completely depopulate the tank, but it can happen. This parasite can spread fast and infect even the largest aquariums in a matter of days.

It only takes up to 3-4 days for the parasite to complete its life cycle, provided environmental temperatures are higher than 75 F, which they usually are. Especially with tropical fish that are in need of warmer waters.

This pathogen is also quite aggressive as it undergoes 4 distinct developmental phases: theront (infectious stage), trophont (feeding stage), protomont (drop-off stage), and tomont (reproductive stage).

Some people skip the protomont stage and only mention the other 3. That’s because this stage is the shortest since the protomont will turn into a tomont as soon as it latches onto a hard surface.

The trophont stage is where all the damage occurs, as the parasite consumes the flesh of its hosts, leading to massive damage and death.

It only takes approximately 3-4 days for death to occur, during which multiple or even all your fish can die.

So, after that’s done, despite all your efforts to prevent it, what should you do to reset the tank?

Consider the following:

Use Time to Your Advantage

You already know by now that Ich is a parasitic agent. So, by definition, it requires a host to survive.

The parasite itself will die off if there are no other fish to infect, which only leads to an inevitable conclusion – Ich will eventually die on its own.

You only need to keep the tank running and let Mother Nature follow its course. The parasite is incredibly resilient, though, and it may take several weeks to a month for the pathogen to disappear completely. This isn’t a problem if time is on your side, but it is if it isn’t.

If you can’t afford the waiting game, consider one of the remaining tactics.

Use Medication

There’s a variety of Ich-killing products on the market that you can use. These are designed to attack the parasite in its most vulnerable form – a protomont.

This is when the parasite exits the fish and looks for a hard surface to begin its metamorphosis into a theront. The theront will then swim freely into the water column in search of a viable host.

If the medication doesn’t succeed in killing the protomont in time, it will undoubtedly kill the theront.

You may need to follow a specific cleaning routine, depending on the medication you’re using. It should take a couple of days or slightly more to obtain the ideal effects.

Use Bleach

Bleach is extremely effective at eradicating tomonts (the parasite’s reproduction/incubation phase) before it releases the active theronts.

There are 2 ways of approaching the bleach solution:

Treat the entire tank – A generalized infection results in hundreds or thousands of tomonts spreading everywhere in the tank. This means that the entire tank requires thorough cleaning to remove the pathogens and sterilize the whole environment.

Treat tank components individually – You can use a bleach solution to clean every tank component like live plants, rocks, driftwood, tank equipment, and everything that goes into the water.

A bleach solution of 1:10 concentration should eliminate all tomonts and other forms of Ich everywhere in the tank within 3 hours.

High Temperature

We’re not talking about boiling water, but temperatures high enough to disrupt the parasite’s cycle.

It’s not that the higher temperatures will kill the Ich parasite completely. Instead, it will accelerate its developmental process significantly, boosting its metabolism and lowering its lifespan.

Most people recommend temperatures around 85-86 F for several hours to eradicate the pathogen, but I recommend higher values.

Aim for 90-94 F, especially since there are no fish in the tank to worry about. Maintain the temperature for several hours, and the tank should be completely sterilized.

You can use the same method when treating your life fish as well. In normal conditions, trophonts (the feeding stage) incubate for around 7 days inside the host at temperatures of 75 F.

Increasing the temperature to 85 F may shorten the incubation period to only 3 days. At 95 F, the parasite may die in less than a day or even several hours.

Naturally, your fish are unlikely to withstand such high water temperatures, which is why this procedure is more fitting in fishless tanks.

How Long Can Ich Survive Without Fish?

Ich is an incredibly resilient pathogen that can survive for quite some time in the absence of a host. That being said, the parasite’s lifespan depends on its developmental phase.

We’re only interested in 2 stages: theronts and tomonts. The former is the infectious pathogens that swim into the water in search of a host.

Tomonts are essentially the cysts attached to the tank walls that incubate tomites which grow into theronts.

We don’t discuss trophonts since these only form once the parasite has reached inside the host’s body. We will also skip protomonts, as these are the link between trophonts and tomonts.

So, trophonts turn into protomonts, which swim and attach to the tank’s walls to turn into tomonts.

So, we’re only left with:

  1. Theronts – These represent the parasite’s most vulnerable phase. Theronts will only last up to 24 hours without a live host. This is the main reason why all forms of Ich treatment target theronts specifically.
  2. Tomonts – This represents Ich’s most resilient form. Tomonts are cysts that encapsulate hundreds of tomites which will eventually grow into theronts. Tomonts can survive around 30 days without a host. Some reports even suggest more than 60 or 70 days.

Therefore, it’s safe to say that Ich can still be present in the tank even up to 60 days following your fish’s departure.

Needless to say, treatment is necessary to eliminate the parasite completely from the environment.

Can Ich Survive in Filter?

No, Ich cannot survive in the filtration system. It’s unlikely for the parasite to return to the tank from an infected filter media.

Even so, you should clean the filter along with sterilizing the entire tank for good measure.

Don’t Forget to Cycle the Tank Again

Using bleach and Ich-killing medication in your tank will most definitely result in complete bacterial eradication. So, your tank requires recycling to restore the habitat’s nitrifying and denitrifying bacterial colonies.

The cycling process can last several weeks and should be started from 0, careful not to skip any phases along the way.

Tips for Preventing Ich from Getting Into Your Tank

Fortunately, there are quite a few prevention tactics to employ that are designed to prevent an Ich outbreak.

These include:

  • Quarantine – You should quarantine everything you plan on adding to your tank. This includes fish and plants since these are the most likely to carry the pathogen into the tank. I recommend a quarantine period of 2 weeks for the fish. This is enough to make sure that the fish are healthy and free of any bacteria, fungal infections, and parasites like Ich. When it comes to plants, you can simply sterilize them before adding them to the tank. You can use vinegar or a bleach solution in this sense since these will eliminate all dangerous pathogens and any potential hitchhiking microorganisms.
  • Prevent fish stress – In other words, keep water quality high, prevent overfeeding, and avoid overstocking the tank, among other things. Fish stress is often responsible for triggering an Ich outbreak due to lowering the fish’s immune system. This makes the fish more sensitive to the pathogen, and that’s where all the problems start.
  • Source your fish wisely – Only get your fish from reputable sources. This minimizes the chances of getting weak or infected fish that may already carry the parasite. You can achieve this by informing yourself on trustworthy sources available in your area or online.

This being said, there’s always a risk of an Ich outbreak, despite all your efforts to prevent it. When that happens, it’s your awareness that will make all the difference.

Always monitor your fish to detect early signs of infection, as this will significantly increase the treatment’s effectiveness.


Ich is a deadly parasite that’s capable of depopulating your entire tank. Fortunately, there are many ways to prevent it and even more ways to treat it.

As a closing note, if the infection appears to be generalized, I recommend euthanizing the fish and starting all over again.

A generalized infection is very difficult to combat without massive damage along the way.

Author Image Fabian
I’m Fabian, aquarium fish breeder and founder of this website. I’ve been keeping fish, since I was a kid. On this blog, I share a lot of information about the aquarium hobby and various fish species that I like. Please leave a comment if you have any question.
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