New Tank Syndrome – Symptoms, Causes, & How To Fix It

    New tank syndrome

    Setting up a new aquarium is an exciting process. But it can also be difficult if you don’t follow a few key steps. New tanks are prone to crashing, causing fish to die repeatedly for a few weeks at a time. What is new tank syndrome and what are its causes?

    New tank syndrome occurs when you add fish to a new aquarium. Fish produce ammonia and other waste products that your filter is not able to fully process yet. Pollutant levels rise dangerously, causing fish to die.

    New tank syndrome is frustrating to deal with. But with a little extra knowledge and patience, you can get it under control!

    What Is New Tank Syndrome?

    New tank syndrome has a long history in the aquarium hobby; as long as we’ve been keeping fish tanks, in fact. The first aquarists noted that there seemed to be a “settling in” period of several weeks when starting a fish tank.

    During this time, fish seemed much more prone to dying. But older aquariums seemed to have fewer fish die. Even when new fish are added to them, the tank environment remains stable.

    There is no mystery pathogen, toxin, or another culprit behind new tank syndrome. It’s actually the result of a nitrogen cycle that has not fully established itself.

    We often think of fish waste as something to be removed during water changes. Or your filter picks it up and holds it until you change the pads.

    In reality, fish poop immediately starts to break down in aquarium water. Fish also release ammonia, the most toxic waste compound to aquatic life.

    In a new aquarium, ammonia concentrations rise very quickly. They can become toxic in just a few days if you add too many fish at a time. This causes a sudden death in your fish. Which causes ammonia and nitrite levels to rise even more as they decay.

    This initial difficulty in getting an aquarium running is new tank syndrome.

    New Tank Syndrome Symptoms

    New tank syndrome symptoms
    School of Ember Tetra (Hyphessobrycon amandae)

    If you suspect your fish are dealing with new aquarium syndrome, there are some reliable signs. The symptoms are the same as ammonia and nitrite poisoning:

    • Listless behavior
    • Clamped fins
    • Pale or discolored skin
    • Gasping at the surface
    • Discolored gills
    • Lack of appetite
    • Inflamed blood vessels
    • Eventual death

    Many of the signs of stress in betta fish also apply to other fish suffering from new tank syndrome.

    Causes of New Tank Syndrome

    New tank syndrome happens when ammonia and nitrite levels don’t diminish through an aquarium’s natural biological process. Filter bacteria take a few weeks to culture in a healthy aquarium.

    In the meantime, fish are vulnerable to rapid spikes in pollutants since your nitrogen cycle hasn’t been established yet.

    What’s more, each of the following can make new tank syndrome even worse for your fish:

    • Starter Fish Death
    • Excess food
    • Lack of filtration

    All three of these result in decaying organic matter being left in your aquarium water. This organic matter feeds bacteria that raise ammonia and nitrite levels.

    Beneficial Bacteria And The Nitrogen Cycle

    In a mature aquarium, there are micro-organisms that actually eat ammonia. Nitrifying bacteria in the genus Nitrosomonasfeed on it, converting it into nitrite (NO2-). Nitrite is less toxic to fish but it is still a sign of poor water quality.

    Fortunately, a second set of bacteria eat nitrite, converting it into nitrate (NO3-). Nitrate is well tolerated by aquarium fish (though invertebrates are still sensitive to it). Depending on the species of fish, levels below 20 to 40 ppm are safe.

    Nitrate normally collects in an aquarium until you remove it with water changes. It also serves as fuel for plants and algae, though they prefer ammonia and nitrite.

    There is a third set of bacteria; de-nitrifying bacteria, that feed on nitrate. They convert it to nitrogen gas (N2), which passes into the atmosphere.

    These bacteria are anaerobic, meaning they are allergic to oxygen. You need areas with oxygen-poor conditions for them to live in large numbers. In a healthy aquarium, these places are rare. It’s best to rely on water changes and plant activity to remove nitrates.

    Understanding the aquarium nitrogen cycle is crucial to getting an established aquarium. So I’ve included a video here that breaks the subject down even further for you:

    YouTube player

    How To Fix / Cure New Tank Syndrome

    How to fix new tank syndrome
    Angelfish (Pterophyllum scalare)

    Once you’ve identified that your new tanks are suffering from new tank syndrome, you will need to take rapid action. Otherwise, your fish will die quickly.

    Supplies Needed:

    Step 1: Use a test kit that measures all three of the nitrogenous waste products (ammonia, nitrite, nitrate). Test your water quality to identify which parameter is dangerously high.

    The results will be elevated ammonia levels, ammonia + nitrite, high nitrite, or nitrite + nitrate. If only ammonia is high, it means you don’t have any of the nitrifying bacteria yet.

    Ammonia + nitrite (or just nitrite) means that the first set of bacteria is present and consuming ammonia. But the second set that consumes nitrate hasn’t been fully established.

    If you see just nitrate present and you are doing a fish-less cycle (see below), add extra ammonia so your first set does not die.

    The presence of nitrite + nitrate means that both sets of bacteria are present. While the water quality may still be too dangerous, you have established beneficial bacteria now.

    Step 2: Perform a water change. If your nitrogenous waste levels are very high, do a 50% water change. For lower levels, do a 10% to 30% water change.

    Step 3: Refill the tank using dechlorinated tap water. Make sure that you choose a brand that does not also detoxify ammonia or nitrite.

    We need trace amounts of these pollutants to feed our slowly maturing bacteria. If you remove all of their food, you make it that much harder to get a mature filter running.

    Step 4: Retest your aquarium water. If nitrogenous waste levels remain dangerous and there are fish present, do another water change. Keep doing them until nitrogenous waste levels are brought down to safe levels.

    Step 5: Once your pollutant levels are at safe levels, only feed sparingly. If you can, remove excess fish. Only a few fish are needed to provide a source of ammonia for bacteria. Test your water daily and be ready to do more water changes if needed.

    How To Prevent New Tank Syndrome

    Severum Cichlid (Heros severus)

    New tank syndrome is preventable if you know what to expect from the very beginning. But in case you weren’t warned by the folks who sold you your tank, here are some tips to keep it from happening!

    Fishless Cycling

    Adding fish is the traditional way to cycle an aquarium. But it’s not the only way. Fishless cycling is becoming more popular because it is safer for any animals introduced to your tank.

    Another advantage of fishless cycling is that you don’t have to worry about your parameters becoming dangerously high. No water changes are required, regardless of the concentrations. Live fish make cycling a tank much more complicated.

    So instead of relying on live fish waste for ammonia, you can simply add your own! Dr. Tim Aquatics is one producer of pure ammonia.

    Make sure that any ammonia you use is 100% pure. Companies that make ammonia for cleaning purposes often add perfumes, surfactants, and other agents. All of which are toxic to aquarium fish.

    To cycle the tank, start by adding enough ammonia to your aquarium to bring levels up to 5 ppm. An aquarium ammonia test kit is needed to reach the right value.

    Ammonia levels will slowly drop over the course of a week. A sign that nitrifying bacteria have colonized the tank from the air. Once this happens, start testing for nitrite.

    Nitrite levels will spike, and then start to diminish. This tells you that your secondary bacteria are creating nitrate. Once both ammonia and nitrite levels are safe, you can add a few fish!

    Purchase Beneficial Bacteria

    Beneficial bacteria normally take weeks to create a large biological capacity for your aquarium. These days, you can buy pre-cultured bacteria to jump-start your biological filter capacity!

    Bottled beneficial bacteria can speed your cycling process to complete in as little as a few days. The bacteria quickly find their way into your filter and substrate and start breeding.

    You will need slightly elevated ammonia and nitrite levels for their food. A few fish being lightly fed will get them started.

    You can also combine this with the fishless cycling method to speed up cycling even further. These bacteria do exist everywhere in the world. But adding them yourself will have your tank fully cycled in at most a week.

    Use An Aquarium Test Kit

    New tank syndrome can catch you by surprise if you aren’t actively testing your water. Since toxic waste compounds don’t have a smell, you need to measure water quality using a test kit. The API Master Freshwater Test kit is the one I always recommend.

    It has liquid reagent tests for ammonia, nitrite, and nitrate. Liquid reagent tests are much more accurate than color-changing test strips.

    Slightly misreading your nitrite or ammonia levels is the difference between a mature tank ready for fish. And one that’s still in the grips of new tank syndrome.

    Add Biological Filter Media

    Lastly, you can buy media designed specifically to culture nitrifying bacteria. Ceramic biological filter media is my favorite. It’s inexpensive, lightweight, and easy to add to any canister or power filter.

    Any good biological filter media also has a huge total surface area. This is important since bacteria, being microscopic, will coat any surface. The more surface area available to them, the more bacteria can live there.

    The pores of ceramic media allow bacteria space to live. As well as places for water to flow, carrying ammonia and nitrite to them.

    Filter bacteria will still live inside of a filter with no biological media built in. But you will have a more robust colony purifying your tank water using biological filter media.

    Can New Tank Syndrome Kill Fish?

    New tank syndrome is a leading cause of fish death for beginning aquarists. Nitrogenous waste products are highly toxic compounds that normally exist in trace amounts in nature. Sometimes they aren’t detectable at all when using test kits.

    The amount of water and space for natural biological processes that remove pollutants in nature is huge compared to the number of fish. Any aquarium is far more crowded than a natural environment.

    Toxic ammonia levels can rise very easily, even in mature tanks. Nitrite and nitrate are less toxic compounds.

    But they can still kill fish if allowed to rise unchecked. Invertebrates like corals and shrimp are even more sensitive than fish to these pollutants.

    Monitor your pets for signs of nitrite and ammonia poisoning on a daily basis.

    How Long Does New Tank Syndrome Last?

    New tank syndrome will last as long as it takes to get the nitrogen cycle established. Even if you repeatedly lose fish, you will still have a mature aquarium in 4-6 weeks. Fish death is unfortunate. But it won’t impede the cycling of your aquarium.

    Adding the beneficial bacteria yourself can bring new tank syndrome to an end in as little as a week.

    The bottled bacteria won’t cause ammonia levels to immediately drop, however. You will still need to do water changes to preserve any fish you currently have.

    Can New Tank Syndrome Occur In Mature / Established Fish Tanks?

    Rainbow fish (Melanotaenia boessemani)

    Yes, it can occur in mature tanks! It is rare since beneficial bacteria are very hardy. And they have an endless supply of food from your fish. But there are three ways that new tank syndrome often occurs in older aquariums

    1) Aquarium/Filter Spring Cleaning

    The most common way is when an aquarist decides to do a full “spring cleaning.” They take out the fish, all of the water, all of the rocks, gravel, etc. They give the filter a complete scrubbing and remove all of the slime from the interior surfaces.

    And then they add their freshly cleaned rocks and gravel. Before dumping all of their fish back into the tank with clean water. Everything looks pristine and beautiful. Except they’ve forgotten about their poor beneficial germs, which have been exterminated.

    A spring cleaning completely resets your nitrogen cycle. You have a new aquarium again. Which has no beneficial bacteria to consume all the waste your fish create.

    I never recommend doing a full spring cleaning. You can still change your substrate or even do a deep cleaning of your filter. But never do both at once.

    It’s a good idea to “seed” a cleaned filter with a piece of the old filter media. It’s rich in bacteria that will jump-start the new colony.

    Also, use as much of your old aquarium water as possible. Save it in buckets to fill the clean tank with. It has millions of bacteria that will keep your nitrogen cycle going.

    2) Broad-spectrum Antibiotic Medications

    Antibiotic medications are great if you need to kill bacteria that cause disease. Columnaris, vibrio, and other germs all respond well to medications. But be careful when using antibiotics. Beneficial bacteria can also be affected or even eliminated.

    This depends entirely on the medication in question. It’s more common with older fish medications. These days, even broad-spectrum agents like Melafix won’t reset your nitrogen cycle.

    This is another reason why I recommend using a quarantine tank to treat a sick fish. Medicating fish in a separate small tank saves medication, for one. You also won’t be harming your good bacteria or more sensitive animals.

    3) Extended Power Outages

    This last one is often a mystery killer for hobbyists. Power outages can cause new tank syndrome to arise if they last for a long time. I’m talking several hours to over a day without power.

    How could this happen? Nitrifying bacteria are aerobic organisms. Meaning they need oxygen levels to remain high. During a power outage, water flow stops to your filter unit. In a power filter, there is usually enough airflow for your filter bacteria to survive.

    But canister filters are sealed and airtight. Plus, dissolved oxygen levels in water are on average 1/100th that of atmospheric air. If the power goes out your filter bacteria will quickly consume what oxygen there is. And then suffocate and die.

    This is a partial reset of your nitrogen cycle. There are still beneficial bacteria scattered in your aquarium water and substrate. But there may not be enough bacteria to keep the nitrogen cycle process operating at full capacity.

    If you run a canister filter, it is a good idea to have a spare bottle of nitrifying bacteria on hand. Just in case of a power outage!


    New tank syndrome is a difficult process to deal with. We don’t want to see our pets suffer and die. Which can seem mysterious if we aren’t familiar with how the nitrogen cycle works.

    Fortunately, this guide will have armed you with all of the knowledge you need. New tank syndrome need not be impossible to deal with!

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