New tank setup, crypts, rotala, and saggitaria

What Is New Tank Syndrome: Cause, Symptoms, Solutions

Starting a new tank can be tough, especially when you hear:

“You’ve gotta wait for the tank to cycle before putting any fish in. At least for a week.”


No pretty bettas or cardinal tetras for a week or more? But the aquarium is already set up!

The thing is that certain natural processes must be established even in the artificial environment of a glass box. They can be sped up with certain products, but a degree of patience is a necessity.

New tank syndrome occurs when an aquarium doesn’t have beneficial bacteria to break down ammonia and nitrites. These two invisible chemicals can poison livestock. Bacteria that detoxify them live on aquarium filters, substrates, and plants. But these bacterial colonies take time to grow and mature.

They may take 2-8 weeks to grow sufficiently. Even with starter bacteria products or ammonia dosing, their reproduction cycle is relatively slow (24-48 hours spawning).

Among budding aquarists, new tank syndrome is a widespread occurrence that leads to the death of many fish. It can kill the desire to keep fish altogether.

What’s more, even mature tanks can experience new tank syndrome if the beneficial bacteria die out.

Let’s explore in depth what new tank syndrome is, how to deal with it, how to speed up the process, and how to prevent it from happening in established tanks.

What Is New Tank Syndrome

Fishkeeping is a quiet hobby and patience is an intrinsic part of it. Possibly, the most difficult time to be patient is upon starting a new tank.

Buying the tank itself and setting it up is all super exciting, full of mystery, creativity, and barely contained anticipation. And when everything is put in place, filled up with dechlorinated water, and ready to accept its new inhabitants, the local fish storekeeper tells you that it cannot safely house fish yet.

Or worse, they sell you a bunch of products to get the nitrogen cycle going without warning you about the consecutive steps.

New tank syndrome refers to a tank that lacks (sufficient) beneficial bacteria. Healthy amounts of Nitrosomonas and Nitrobacter bacteria break down ammonia (NO2) into nitrites (NO3), and then nitrites into nitrates. The transformation of ammonia into nitrates is what the nitrogen cycle is, in a nutshell.

Fish are much more sensitive to ammonia and nitrite buildups in the water column. Nitrates also will harm them but much more slowly and at a much higher concentration. A newly set up tank doesn’t have enough beneficial bacteria to create these chemical metamorphoses at a sufficient rate. 

Bacteria drive the entire process and when their numbers are low, new tank syndrome will occur.

New Tank Syndrome Symptoms

The symptoms of a new tank syndrome are largely identical to ammonia poisoning:

  • Lethargy
  • Lack of appetite
  • Bloody gills
  • Gasping for air at the surface
  • Foul water

Death will occur if these obvious signs of stress are not addressed quickly.

Somewhat counterintuitively, larger fish may exhibit some or all of these symptoms sooner than smaller individuals. Bigger bodies require have more powerful metabolism and that can lead to increased absorption of ammonia and nitrites.

That’s more of a guideline than an inevitability as different species have different tolerance toward ammonia and nitrites.

How to Start the Nitrogen Cycle in a New Tank

There are several ways to make a new tank safe for livestock. 

The simplest is to wait, with the filter running, for two months. Bacteria live all around us, they will find their way to your tank, even if it has a lid.

But there are ways to speed up the process a bit.

Starting Bacteria

Nowadays, many fish stores can sell you a vial of starting bacteria. It is a concentrated colony of bacteria that will kickstart the process and will shorten the whole process.

If you go this route, still, wait for at least 10 days before adding your first fish. Some stores may offer you starting bacteria and detoxifying liquids that remove ammonia and nitrites.

While having those is certainly helpful in the long run, using them early on to stabilize the water is risky. It is better to invest your starting budget in reliable reagent tests to measure ammonia and nitrite levels and wait for them to go down by themselves.

This would ensure that the nitrogen cycle is truly underway and that adding fish is safe.

Always add a few (inexpensive) fish at first and observe them carefully for any signs of stress. If they are healthy for a week, you can add a new batch but don’t overstock the tank early on, as beneficial bacteria take time to colonize everything. Adding too many fish early on can overwhelm the bacteria’s capacity to process waste.

In turn, this would break the nitrogen cycle, leading to mass death.

Add Ammonia

There are ammonia products, too. Ammonia is the main food for Nitrosomonas bacteria that break it down to NO2, nitrite.

However, paying for concentrated ammonia is largely a waste of money.

A better idea is to buy fish food that you are going to be using anyway, once the tank is populated. “Feed” the empty tank a tiny amount of food for the first 3-4 days. The fish food will start decaying, releasing ammonia that, you guessed it, will feed the bacteria.

Add Filter Media from Another Tank

If you have an established tank, getting a piece of its filter media for the new tank is a great way to shorten the waiting period and avoid new tank syndrome.

Essentially, the media from an established tank is chock-full of the desired bacteria. The same goes for its hardscape and substrate, which can also be transferred over.

Just make sure the established tank is completely free of pathogens, as they will travel across as well.

I’ve started new tanks in as few as five days by adding the sponge filter of an old tank.

Can You Add Fish in a Brand New Tank?

Adding a fish or two to a tank that is not fully cycled is possible, albeit a bit risky. Fish waste will help bacterial growth, but you must change the water regularly to keep the fish alive.

This is known as fish-in cycle, but it can harm the fish if left unattended.

Fishless cycling is way safer, even if it is more boring.

How Long Does It Take for New Tank Syndrome to Go Away?

A new tank will always take some time before it is safe for fish or shrimp. Even sturdy species like betta can die from a new tank syndrome if put too soon into the aquarium.

To be on the safe side, it is best to wait 6-8 weeks before adding fish.

Purchasing a flask of starting bacteria from your local fish store will get the bacterial colonies going, but they need time to grow more and spread. High-quality starting bacteria can make a tank safe-ish for a few sturdy fish in a week, but waiting for two weeks is much better.

Depending on the tank size, its filtration system, and the presence of substrate and plants, the bacterial colonies could take over two months to grow to the necessary levels.

Increasing water temperature to 26°C or 78°F helps bacterial growth as warmer water speeds up their metabolism.

Introducing live plants from day 1 also helps because plants consume nitrates and complete the nitrogen cycle. Decaying leaves are another source of ammonia that feeds the Nitrosomonas bacteria.

When the water tests become stable, start adding fish. However, add a few fish at a time, to ensure that the filtration is adequate and can handle their waste.

If you add too many fish too quickly, the beneficial bacteria may be insufficient to break down all the poop and ammonia excess, leading to fish death.

New Tank Syndrome in Established Tanks

Mature aquariums can experience unhealthy NO2 and NO3 levels, too. Even though new tank syndrome becomes a bit of a misnomer in that case, the symptoms and the underlying cause are identical.

Established tanks can lose their population of beneficial bacteria in the following ways:

  • Washing the filter under tap water
  • Replacing all filter media at once
  • Filter malfunction
  • Too thorough cleaning
  • Medication
  • Overstocking

Overfeeding is another way to overwhelm the beneficial bacteria and to poison your fish.

Washing Filter Media Under Tap Water

Filter media should never be washed under tap water. Chlorine, even in small quantities, is deadly to all bacteria. That’s the very reason why it is put in tap water.

Gently wash the filter media in the dirty aquarium water. Once you siphon out a bucket of water, wash the filter there. Don’t be overzealous with cleaning it completely. It is enough to ensure its smooth functioning for a month or two, as too much scrubbing will also remove a lot of bacteria.

Filter Media Replacement

Replacing all filter media at once basically removes all bacteria from the tank.

Don’t ever do it.

If the filter media is a sponge, put the replacement sponge to float in the aquarium for a couple of weeks. This will allow enough time for beneficial bacteria to colonize it.

If the media are stones or other hard particles, replace them gradually, over several weeks.

Filter Malfunction

If the filter breaks or remains unplugged after maintenance (we’ve all done that; more than once), it won’t be able to purify the water.

Submerged filters will still help, as the colony of beneficial bacteria stays within the fish tank, but canisters and hang-on filters become useless when turned off.

The presence of substrate, rocks — lava rock is excellent for bacterial life — and plants offsets the lack of filter to an extent. In fact, a densely planted tank could go without a mechanical filter for long or even for good, but planted tanks require special lighting and, often, substrate.

Respectively, a bare bottom tank provides very few places for bacteria to grow. A decoration or two, and the filter are the only viable colonies. Carefully cleaning the filter and ensuring its smooth operation are paramount to sustaining a bare bottom tank properly cycled.

Deep Cleaning

Cleaning your aquarium regularly, especially until it matures, is necessary to prevent ammonia build-ups. Weekly water changes in the first six months, substrate vacuuming, and the occasional washing of the filter are part of the routine.

However, cleaning the tank too thoroughly could harm the beneficial bacteria.

Washing hardscape and siphoning the gravel too deeply and too often could destroy bacteria.

If you must perform a tank reset or something equally serious, keep your livestock in a quarantine tank for a few weeks. Allow the restarted or deeply cleaned aquarium to stabilize again before returning them into it.


Medication may be necessary and sometimes it makes sense to administer it directly into the main tank. Ailments such as ich spread throughout the water column and hardscape, so medicating the entire tank may be the best way to tackle it.

However, having a hospital tank ready to accept sick fish is always a good idea. Setting one up isn’t all that hard, and it can keep the beneficial bacteria in your main tank alive.

See, many fish medications are antibiotics. They are designed to kill microbial life and don’t distinguish between pathogens and beneficial bacteria. They kill ‘em all.

Always read the instructions and administer medications carefully. Don’t overdose and don’t use them longer than recommended. Don’t mix meds either.

Monitor ammonia and nitrite levels while medicating and in the days after the active treatment.

Aquarium salts are an exception to the rule, though. They can alleviate a lot of conditions if used correctly, without wiping out bacterial colonies.


Adding too many new fish too quickly can overwhelm your tank’s capacity to process ammonia.

Usually, when considering how many fish to add to a tank, hobbyists and shopkeepers talk in terms of space and water volume. That’s understandable, as these things are much easier to measure.

However, filtration, plant matter (not because plants can kill fish but because they can filter the water), and other tankmates play crucial roles too. A very important aspect of any composition in a community tank is the level of pollution produced.

That’s one of the main reasons why you should always add a few fish at a time and never many at once. Many new inhabitants mean new dynamics in your fish tank.

Drastic changes in the precarious balance of a boxed ecosystem usually lead to unwanted results.


Overfeeding is extremely common among budding fishkeepers. It can kill your fish in many ways; ammonia spikes are much more likely to occur if food regularly stays uneaten.

Feed your fish sparingly. As long as they grow, their fins are intact, and their colors are bright, they get sufficient sustenance. Keep in mind that bright substrates might affect fish coloration and no diet will change that.

Quick Fixes for New Tank Syndrome

Dealing with a new tank syndrome in an actual new tank requires patience, more than anything else.

Give it time, keep the temperature stable, change 25% of the water every week for the first two months, and test for ammonia and nitrites.

When things go astray in an established tank, with fish and other livestock, measures must be taken right away.

  • Water change — 30%-50% water change may be necessary to tackle ammonia or nitrite spikes right away. If one change is not enough, perform a second the next day. Changing massive amounts of water comes with its own risks, so it is better to spread them across several smaller changes, if possible.
  • Siphon the substrate — Removing waste from the aquarium floor eliminates ammonia sources.
  • Clean out dead leaves or fish — Dead plants or fish decay, producing ammonia. Cut out any yellow or brown leaves and take out any dead fish right away.  
  • Add an airstone — Adding an extra oxygen source helps fish breathe and beneficial bacteria grow.
  • Increase temperature — Increasing the temperature to 26°C or 76°F will boost bacterial growth. Do that after you’ve vacuumed the bottom, as higher temperatures also speed up decaying processes and the amounts of ammonia released.
  • Don’t feed — Stop giving food to the fish for a few days. They can handle it and will produce less waste (and there won’t be any excess food to decay).
  • Use water conditioners — Water conditioners like Seachem Prime reduce ammonia and nitrites in the water column and can provide a quick fix to a new tank syndrome.
  • Use aquarium salts — Salts detoxify nitrites and can help fix the issue quickly.
  • Don’t use terrestrial fertilizers — A majority of fertilizers for terrestrial plants release large amounts of ammonia. Don’t use them to boost your aquatic plants if you have any livestock.
  • Drop the pH level below 7.0 — Low pH levels convert the highly toxic ammonia into ammonium. Similar, granted, but much safer for fish. However, use this approach if you are sure that your fish can handle lower pH. Then, lower it slowly, no more than 0.5 per day. Otherwise, the fish can enter pH shock, which can kill them faster than ammonia poisoning. What’s more, not everyone can do that. Water with high KH will resist most attempts to acidify it.

Be Patient and Wait for the Tank to Establish a Nitrogen Cycle

It can be frustrating to wait a few weeks more before getting that awesome new betta or angelfish, but it is necessary.

New tank syndrome is a real killer and a bit of patience goes a long way in making your fish healthy and happy. Also, populate your new tank slowly, allowing it to build up the adequate capacity to process waste..

The thing is that it can occur in matured tanks as well. Luckily, there are a few quick fixes to help tackle it before the signs of high nitrite or ammonia levels become too severe.

As scary as it sounds, with a bit of patience, adequate aquarium stocking, and without overfeeding the fish will be well isolated from the new tank syndrome.

Similar Posts

Leave a Reply

Your email address will not be published. Required fields are marked *