It’s the worst possible thing that can happen to a first-time aquarist: you excitedly set up your brand-new tank and fill it with colorful fish, only to find them all dead or dying the next morning. What happened? It’s probably new tank syndrome.
We can’t bring your fish back, but we can explain what happened — and help you save any survivors.
What is “new tank syndrome”?
→ The short answer: New tank syndrome refers to the sickening and dying of fish and invertebrates in a new aquarium due to a lack of waste-eating bacteria.
→ The long answer: If this is your first time setting up an aquarium, you may not be aware that all fish tanks need to “cycle” without fish for 4–8 weeks after filling them up. Although some unscrupulous pet stores might tell you otherwise, this means bringing home fish on the same day you buy the tank is out of the question.
As we explain in our full post on how to cycle an aquarium (a must-read if you’re not familiar with this concept), beneficial bacteria colonize the filter and substrate during this natural process. These microorganisms are crucial because they’re the only thing aside from water changes that can remove waste from the water column. If they’re not present, the tank’s inhabitants become ill or even die from swimming around in their own waste.
“New tank syndrome” is technically not entirely accurate, as it can also happen in established aquariums. A large swing in the water’s pH (acidity) level, replacing the entire filter cartridge, a power outage, using water that wasn’t dechlorinated, and other major disruptions can cause the beneficial bacteria to die off.
Did you know? Overstocking or adding too many fish at once, especially in newly cycled tanks, can also cause a regression. We tend to call this an “ammonia spike”, however, because the beneficial bacteria didn’t actually die — they just became overwhelmed.
Symptoms of new tank syndrome
New tank syndrome can come as a huge shock and completely puzzle new aquarists. It’s not unusual to lose all your fish within a few hours or overnight. Once you understand the nitrogen cycle, however, this syndrome becomes easy to diagnose.
You may be dealing with “new tank syndrome” if:
- The aquarium is less than ~2 months old
- You never “cycled” the aquarium
- Your fish are lethargic, refusing to eat, gasping at the surface, or dead
- The aquarium water is cloudy or smells foul
- The aquarium is older but was recently disturbed
If all your fish have died, you can simply follow normal aquarium cycling instructions. This will ensure the water is safe before you add any more. If they’re still alive, the instructions below can help keep them that way — though we can’t make any definite promises.
Treatment for new tank syndrome
Step 1: Water test
Did you know that treatment for 99% of aquarium-related problems starts with a water test? If you don’t own an aquarium test kit containing at least tests for ammonia, nitrite, and nitrate, you should head out and get one right now*. Not tomorrow or next week, but now! A liquid kit is preferable due to its much higher accuracy, though strips can be helpful in a pinch.
We know they’re expensive. We know performing a full test panel takes time. But take it from us: a water test kit is non-negotiable and almost as important as the tank itself.
Test the aquarium water as soon as possible. Any ammonia or nitrite reading (meaning anything above 0.0 ppm) confirms that you are indeed dealing with new tank syndrome
*If you’re headed to your local fish store, pick up some bottled beneficial bacteria as well. They’re usually called something like “Safe Start”, “Quick Start”, “Stability”, etc. and most pet/aquarium shops carry them.
Step 2: Mitigate
A magical solution to NTS exists: returning your fish to the store and trying again once the aquarium is cycled. Unfortunately, however, most stores don’t accept returns for live animals. Worth a try, though!
If the aquarium store won’t take back the fish, all you can now do is try to mitigate the damage while the beneficial bacteria establish themselves. Luckily, there are a few things you can do that might just help your finned friends pull through. In case it wasn’t clear yet: do NOT add any more fish.
The following steps are non-negotiable if you want to save your fish:
- Read the cycling guide. You need this information to interpret your water tests and understand what’s going on in your aquarium.
- Check that the filter is actually running and functioning properly. Don’t disturb it otherwise.
- Test the water daily. It’s the only way to know whether the NTS is passing.
- Perform a ~20% water change with dechlorinated, temperature-matched water if ammonia reads more than 0.5 ppm or nitrite more than 1 ppm. You may have to do this daily for a while.
- Reduce feedings to no more than a pinch or so a day. More food means more waste and a greater risk to the fish. They can even go for a few days without any food.
The following steps are optional but recommended:
- Dose bottled beneficial bacteria according to the instructions on the packaging.
- Ask someone you know who has a cycled aquarium for some filter material to “seed” your bacteria population. Transport in a tub of aquarium water with an air stone to prevent the bacteria from dying en route.
- Add an air stone to the tank and point the filter outflow at the surface to increase oxygenation. Toxic ammonia and nitrite make it harder for fish to breathe.
- Use an ammonia detoxifier like Seachem Prime. Always follow the instructions on the bottle! If used correctly, it will not slow the cycle and can help keep your fish safe.
💡 We have to be frank with you: cycling an aquarium while trying to keep the fish inside alive is a frustrating and slow process. The constant water changes are important to save your pets, but they do slow down the beneficial bacteria. Just keep up those tests and those water changes; we promise it’ll stop eventually.
You’ll know your aquarium is cycled (and your fish in the clear) when you consistently get a nitrate reading on your test and the ammonia/nitrite stays at 0 ppm. At this point, you can reduce the water changes to a normal maintenance pattern and start slowly(!) increasing to a normal amount of food for your fish. Don’t add any additional fish just yet, though, and keep testing daily for at least a week.
Conclusion
New tank syndrome is one of the most frustrating things that can happen to an aquarist, especially if this is your first tank. You’re so excited, and then… mayhem. Take a deep breath and read the cycling guide to understand what happened. If any of your fish are still alive, the instructions above might just help them pull through.
