Aquarium Tank Crash – What Is It & Can it Be Avoided?

Most of us have been lucky enough to catch any errors or problems with our aquarium to prevent a catastrophic ending to our pride and joy. But for those who have been away, or not paying attention, a total loss of corals, fish, or both is completely devastating!

A tank crash is when a rapidly occurring event happens within an aquarium. They often happen without warning and are commonly caused by a biological imbalance. It is usually too late to do anything to prevent it by the time od discovery and is usually followed by a complete restart of the aquarium.

Tank crashes force many people to leave this hobby mainly due to their lack of experience or attention and causing the crash. For the rest of us, however, it is a great opportunity to pick up some great bargains on the second-hand market!

Many people do re-start their aquarium again, hopefully learning from their mistakes and proper research and education is key.

Let’s look at some of the most common things that can lead to a tank crash so you can now avoid them…

What Causes Tank Crashes?

Every aquarium crash can usually be attributed to one of the following areas:

  • Human Error
  • Contamination
  • Equipment Failure
  • Chemical Imbalance
  • Lack of Maintenance
  • Mother Nature

Each of these categories contains some of the simplest errors, but they can have terrible consequences.

Tank Crash from Human Error:

Too Much, Too Soon

You have tried to add too many fish or corals too soon in the life of your aquarium. The Beneficial Nitrifying Bacteria are not in the quantities to cope with the bio-load and you have a huge Ammonia spike killing your inhabitants.


We are all bad for this! Having a beer or wine while doing maintenance and forgetting or miscalculating something. When do you normally catch the error? The day after when it can be too late! Save the booze until after the work is complete!

No Alcohol Sign

Dosing A Chemical You Shouldn’t

There is an old saying that if you can’t test for it, then don’t put it in. This is sound advice. However, there are times when you need to dose a medication like Chemiclean or similar.

Make sure you follow the instructions to the letter and research it as much as you can before using it. Many people before you will have used it and they will have published their results on the forums. Take a generic view and see what the most common answers seem to be.

Over Dosing

This causes more tank crashes than anything, especially mis-dosing Alkalinity. Before you change anything on your dosing regimen, be sure your test result is accurate.

Make any changes in small increments to prevent a rapid change in a water parameter. Test often to ensure what you want is what is happening!

Tank Sitter

An inexperienced tank sitter can cause you more harm than good while you are away on vacation. Try and find a fellow aquarist who you can train on your system to look after your tank. Lack of experience or not being able to spot a problem can easily lead to a tank crash.

For more information and great tips on preparing your aquarium for a vacation, you can read my article HERE…

Trying Something New

Fiddling when you don’t know what you are doing is a sure way to begin a chain of events that can lead to a tank crash. This hobby relies so much on knowledge and there is a tremendous amount of information out there.

Before you try anything new, research, research & research. This entire website is created to help you with that. Just read, learn and then try!

Bad Advice

There is so much of this around, especially on the internet, and to be honest a lot of fish stores. Many fish stores can have inexperienced staff or staff that just want you to part with your cash.

The best advice I can give to any newcomer is to ask questions to as many people as you can and see what the general consensus is for your answer. Over time you will begin to find your trusted sources and then stick with them.

Tank Crash From a Contamination:

Aerosol Sprays

Aerosol Air Fresheners, Stinky Candles, and Misting Devices have been known to cause tank crashes by poisoning the water. Most people will have no problem with these but I have read that some are so concentrated and when released next to the aquarium the Activated Carbon and Protein Skimmer have not been enough to remove the pollutants.

I would advise using caution when using any of the devices in a room containing a saltwater aquarium. They may have been fine for a freshwater aquarium, but the marine environment is more delicate and may prove catastrophic if one of these is used without oversight.

You may find this article helpful: ‘Are Candles, Scented Oils & Air Fresheners Aquarium Safe?

Contaminated Water

Never ever put water from a bag into your aquarium. Water from another aquarium could contain any number of treatments or contaminants that could kill your tank.

You could purchase a fish from a store who is treating it with copper. Add copper to your aquarium and say goodbye to all your invertebrates!

Untreated supply water from your city or well. I live on a lake and I can smell an earthy tone in our house water after heavy rainfall. But my RO/DI unit produces 0 TDS all of the time and I’m not worried. An RO/DI water filter will be one of the best investments you ever make for your aquarium

Find out more information in my article How To Select An RO/DI System For Your Aquarium.

Dirty Hands/Arms

This is a common one. The majority of us use body washes and scented soaps to wash with. There can be traces left on our skin as we put our arms into the tank.

Have you been at work and forgot to wash your hands and arms before ‘Quickly Fixing’ something in the tank.

Contamination can happen quickly or be the catalyst to something more serious in your aquarium.

Tank Crash from Equipment Failure:

Cracked heaters, a heater or chiller sticking in the ‘ON’ position have caused many a tank crash. Replace your heater on an annual basis, buy good quality heaters.

For years I have used and recommended the Eheim Jager Range – link.

Stuck Heater/Chiller

Keep your chiller serviced and maintained and if you can, get yourself at the very least a temperature controller to shut off the device if your water temperature goes out of range.

An Aquarium Heater Controller is a great investment which you can find Here at

An aquarium controller is the best solution but the cost can make them prohibitive to many aquarists just starting out.

You can find loads more information on Aquarium Controllers in my article Here.

Dosing Pumps

A dosing pump not dosing is not too bad but a dosing pump that continues to dose is a big problem. You should keep them maintained and calibrate them regularly. Replace hoses and grease the rollers often to help maintain efficiency.

Mechanical Timer
Mechanical Timer

Dosing pumps that use Plug-In type timers to operate them need to be checked to make sure the time setting has not been accidentally altered. Mechanical Timers with the pins you move in/out should never be used on dosing pumps – They are too easy to accidentally hit.

Find a Good Electronic Timer Here at


Correct installation and setup are paramount with an ATO. A malfunctioning system ATO will drop the salinity in your aquarium rapidly and will lead to a tank crash if left too long.

Ensuring the run timer is set correctly and all the hoses and sensors are securely fastened will prevent most ATO problems.

If you are unsure what an ATO system is you can find out more in my article HERE…

Stray Electrical Current

An electrical current passing through the water can be deadly and if it is small enough can go unnoticed but can slowly cause an imminent death that snowballs into everything dying.

If you feel a shock when you place your hands into the tank its time to investigate every piece of electrical equipment to look for the culprit

Tank Crash – Chemical Imbalance


Ammonia is very toxic to aquatic livestock and it needs to be at zero. Dead, decaying animals & waste will all breakdown into Ammonia if not removed.

Water changes and good husbandry will maintain your Ammonia at zero.

Lack of Gas Exchange

Tightly fitting tank lids, lack of surface agitation or no water movement will prevent gas exchange at the water surface. Nitrogen and Carbon Dioxide need to escape and oxygen needs to be taken in to keep your livestock alive.

Keep the water moving as much as possible, especially during power outages. Oxygen depletion is the first killer during an outage.

Lack of Oxygen

All living organisms need oxygen to survive. You, your fish, your coral, your bacteria all need oxygen and without it, things are going to die quickly.

Algae and medications can strip the water of oxygen, gas exchange, mentioned above all contribute to lack of oxygen.

Water Parameter Imbalance

Keeping your water parameters stable is all you do as an aquarist. You don’t keep livestock, you keep water. Corals are especially susceptible to wandering parameters. Having a parameter like Alkalinity go off the chart is a great way to ensure your coral dies.

Weekly testing is the best way to keep an eye on your water parameters and help you catch anything early.

Rapid Parameter Change

As you may have heard many times, “The only things that happen fast in a Reef Tank is Death” and it is true. Any changes you make must be done gradually. Your aquarium is a finely tuned ecosystem and it needs time to adapt to change.

If you have any parameters changing rapidly you may be lighting the fuse to a tank crash.

Slow and Steady!

Beneficial Bacteria Die-Off

Your Nitrifying Bacteria are your biological filtration that converts the toxic Ammonia and Nitrite compounds into Nitrate and Nitrogen. If they die your tank is going to start heading south.

Lack of oxygen and medications are the two biggest culprits. Make sure you research any medication before you add it to your aquarium!

Keep the little guys alive and keep your tank alive.

Anemones Sucked Into a Powerhead

It happens often and it’s the only reason I do not have an Anemone in my tank. They move and can let go of their grip. Having a reef tank you need strong flow for your corals. Nems will ALWAYS get drawn to a powerhead if they fully let go.

They become shredded and release toxins into the water and there is usually no way back. If you have Anemones then be aware and protect them from the powerhead intakes. You can buy foam collars that help, but you need to clean them daily.

Lack of Maintenance

This is pretty self-explanatory. The majority of the causes previously mentioned can usually be prevented with regular maintenance, good husbandry, and a constant watch for anything arising.

Maintenance can become a chore but you need to find a way to make it easier for you, automate it or find a product so you have to do it less. The easier it is, the more you will do it.

Procrastination is one way to have a tank crash.

Mother Nature

No one can beat her and if it’s meant to be that your tank does not survive her wrath, that’s just the way it is.

Floods, fire, hurricanes, and power outages can only be tolerated so long before your tank reaches a point of no return. Preparation is the key here and the more you can be ready, the longer you tank will survive.

I have a great article on how to prepare your aquarium for a power outage HERE which gives you some great cheap and expensive ways to help.

Can You Stop A Tank Crash?

Generally, tank crashes are hard to stop because the owner is unaware of the situation until they see visible changes with livestock in the aquarium. Usually, by that point the tank crash is imminent and the potential of a total loss can be very high. A rapid water change may be the only help.

If you catch the symptom early enough you can possibly stop the lead up to a tank crash, but a tank crash is really the point of no return.

Good, regular, and proactive maintenance, good equipment, and vigilance are really the only things that can help you spot any problems early and help prevent the road to a crash. Once your tank has crashed, there is no going back.

What To Do After A Tank Crash?

Two options:

  1. Start Again
  2. Sell everything and leave the hobby

I hope everyone chooses option #1 but I know many just didn’t have the time or money to fully dedicate to their aquarium and the crash was inevitable.

Now is the time to begin to plan your new build taking into account everything you have learned. Make some changes and try to make your new tank as easy to work on as possible.

Further Questions

What Is Old Tank Syndrome?

This is generic term used when a mature tank crashes. It can be caused by numerous things that build up over time and slowly increase to a point where if un-noticed could lead to a crash.
Rising Alkalinity, phosphates or nitrates. The build up of Hydrogen Sulfide in a sandbed that is not regularly turned over. The clogging of pumps and pipework causing a drop in flow to your filtration media.
Good maintenance and husbandry will all help to alleviate ‘Old Tank Syndrome’.

Can I Reuse My Sand & Live Rock?

As for your sand and rock, just start again with new sand but if you want to keep your rock you will need to cook it and cure it. Not cooking on a stove! NEVER boil or heat up Live Rock!

Please do it properly and be aware of Palytoxin Poisoning!

Read my article on Palytoxin Poisoning HERE to keep you safe if you decide to keep and reuse your live rock.

Here is a great video from Mark at Melev’s Reef on how to safely cook your Live Rock:


Hi, I'm Richard and I have been an avid aquarist for over 30 years with a passion for Saltwater Aquariums. I love to pass on my knowledge to help others get the same amount a pleasure out of this hobby as I do. View my About Me page to find out more about me & my mixed reef aquarium.

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