New Tank Syndrome: What Is It and How to Fix It (Guide)

Have you ever set up a new aquarium, filled it with fresh water and brightly colored fish, only to have it all fail over the course of two weeks? Maybe you assumed aquariums are simply too hard and gave up for a spell, like so many beginning aquarists do.

What likely happened was that their fish were victims of New Tank Syndrome. And as it turns out, New Tank Syndrome can even affect established aquariums so it’s a good idea to understand the process better!

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What is New Tank Syndrome?

What is the definition of new tank syndrome? This section explains the reasons we see this problem in new aquariums.

The Nitrogen Cycle

Key to understanding how New Tank Syndrome can lead to dead fish is the Nitrogen Cycle. Any aquarist, freshwater or saltwater, needs to know the basics of how nitrogen moves through the aquarium ecosystem. Fortunately, the chemistry is very easy to grasp!

Fish waste, leftover food, and dead organisms break down into, among other things, ammonia (NH3) and ammonium (NH4+). Fish release ammonia from their gills and ammonium as urine; together these two agents are the basis for the Nitrogen Cycle.

aquarium cycle

Water is a source of nitrifying bacteria all over the globe. These organisms can take free ammonia and ammonium and use them for food. A first group (Nitrosomonas bacteria) converts these into nitrite (NO2−).

Nitrite is significantly less toxic than ammonia to animals but will still cause problems in large enough doses. Fortunately, there are also Nitrobacter microorganisms who then take nitrite and convert it into nitrate (NO3−), which is better tolerated by animals in moderate doses.

New Tank Syndrome

So how do new tanks fit into this process? When first setting up an aquarium with clean water you have few to no nitrifying bacteria to convert ammonia to nitrate. When adding fish to such an environment ammonia has a tendency to simply build up rapidly until fish simply die of ammonia poisoning.

The process can seem so mysterious that New Tank Syndrome was the name given to the seeming bad luck that comes with a fresh setup. However there are many ways to avoid losing fish when setting up a new tank!

How Can I Avoid New Tank Syndrome?

How can we avoid or cure new tank syndrome? This section explains what you can do.

Slow Cycling an Aquarium

Most pet stores are going to recommend that you slowly cycle any new tank. The process of growing a healthy population nitrifying bacteria is called cycling. In a mature (cycled) aquarium they form colonies in the substrate and filter but can also be found floating throughout the water column.


Microorganisms surround us like an invisible fog – while these bacteria don’t form spores they exist in soil, dust, non-chlorinated water, and are carried by wind, rain, and in water with your new fish. They will find their way into your aquarium eventually and it only takes one as they reproduce asexually.

However the process is relatively slow; depending on the volume of your tank and how much ammonia is produced, it can take anywhere from 1 to 3 months for your tank to fully mature.

That’s why it’s always recommended to start with a single hardy fish or two before adding more delicate species. Guppies, Bettas, and other hardy, inexpensive fish are commonly used for freshwater slow cycling while Damselfish are perfect for new saltwater aquariums.

In a matter of weeks, you can gradually add fish until your tank is full.

Fishless Cycling

One method that’s less common nowadays is using pure ammonia in a fishless cycle. The benefits include no chance of killing any fish and not having to feed them while the tank matures.

Most fishless cycling regimes rely on 3 to 5 drops of ammonia per 10 gallons along with daily water testing of all three parameters (ammonia, nitrite, nitrate). Once you start detecting nitrite, you can reduce ammonia input to 3 drops per day while continuing to monitor the environment.

Once you have ammonia and nitrite levels close to 0 and detectable nitrate levels you know your aquarium has cycled!

Seeding a New Tank

Another common method of avoiding New Tank Syndrome is seeding an aquarium with bacteria from an established tank. While the amounts aren’t as concentrated as buying bacteria off the shelf, it helps boost the process significantly.

Clipping a chunk of nicely browned cotton filter media from a healthy aquarium is one way to add bacteria to your new filter – simply drop it in or tie it to the new media! We tend to think of the brown muck in our filter as “dirty” when in fact it’s really full of useful bacteria for our aquarium!

Adding plants, rocks, substrate, or even water from an established aquarium also seeds the new one with healthy microorganisms ready to multiply in their new home.

Just make sure that the aquarium you’re seeding from actually is healthy as aquatic parasites like Ich and fungal spores can also be transferred over. Newly added fish are especially sensitive and are ripe for infections.

Buying Cycling Bacteria

Cycling bacteria are so useful that they can be purchased right off the shelf in most pet stores. This is by far the best way to avoid New Tank Syndrome since the agents you need will find their way into the aquarium when they are needed most.

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API QuickStart is a perennial favorite because it works for both fresh and saltwater aquariums, is inexpensive, and jump-starts the cycling process.

Many brands claim that you can add full loads of fish to your aquariums with their products. I don’t recommend this because the bacteria still need time to colonize the substrate and filter. I prefer to build up a fish community over the course of a week, just in case.

Even so, nitrifying bacteria supplements are something every aquarist should have on hand because even established tanks can run into New Tank Syndrome.

New Tank Syndrome in Established Aquariums

New tank syndrome shouldn’t happen in established aquariums…right? This section explains why that isn’t always the case.

Spring Cleaning Your Aquarium

Spring cleaning is something recommended for most animal environments. However we need to be really careful when it comes to aquatic ecosystems because the substrate does more than hold down plants and look nice.

The substrate, rocks, plants, water, and filter are all part of the ecosystem that maintains fish health. And by removing everything to scrub it all clean and adding entirely fresh water, you’re resetting your cycling back to the beginning. If you simply add all of your fish again there is an excellent chance New Tank Syndrome will kill some or all of them!

Here are some tips for managing New Tank Syndrome while doing big cleanings:

  • Save as much of the old aquarium water as possible for reuse
  • Don’t change the filters at the same time as scrubbing the decorations and glass
  • Keep some of your fish in a quarantine tank while your tank cycles once again

Antibiotic Use

The second most common way to induce New Tank Syndrome in a mature aquarium is when fish get sick. Bacterial infections like fin rot are best treated in a quarantine tank because many broad spectrum antibiotics will wipe out nitrifying bacteria populations in your filter, substrate, and water column.

While you may kill the infectious agents you’ve now just created an entirely new problem by crippling the life support of your aquarium!

Make sure you choose medicines that are tailored to specific bacteria, fungi, or parasites, or ideally, move your fish to a quarantine tank for treatment.


New Tank Syndrome can be frustrating and deadly for those unaware of the biological interplay that goes on at all levels in an aquarium. But once you ensure you give as much care to your bacteria as you do to your fish the problem fades into insignificance.

Simply ensure that wherever your fish go nitrifying bacteria have already made a home and you’ll see far fewer issues with New Tank Syndrome!

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