Dead Fish / Tank Crashes / Causes and Avoidance

The absolute worst common aquarium problem is the dreaded tank crash!  There is no worse experience as an aquarist than to have your tankful of fish that you’ve worked so hard to make a good home for wind up dead.  There are a number of reasons why this can happen but with some precautions the danger of unnecessary dead fish can nearly be eliminated.

Dead Fish – Oxygen

Dead Fish -Temperature

Dead Fish -Ammonia

Dead Fish -pH

Dead Fish -Other Factors

Dead Fish – Oxygen

The primary cause of a large number of dead fish is lack of oxygen in the aquarium.  Without proper aeration and water circulation the aquarium can literally become a death trap for the fish in it.  This can literally occur overnight in many cases.  This is why you can not rely on any single source of water circulation and aeration in the tank and two or preferably three separate sources should be used at all times in order to minimize the chances of dead fish due to lack of oxygen.

A hang on back or canister filter is a common primary source of water circulation in many aquariums.  But what happens when they gradually slow down due to becoming dirty or their impeller becomes clogged?  If this is the sole source of aeration in your aquarium then dead fish become imminent.

Monitoring Oxygen can help prevent dead fish.
Monitoring Oxygen can help prevent dead fish.

Salifert Dissolved Oxygen Test Kit

  • Corals and marine fish require very high levels of oxygen concentration because of the low solubility
  • Prevent tank crashes and dead fish by monitoring Oxygen
  • The Salifert Oxygen Profi-Test is extremely fast, measuring oxygen levels in just a few minutes
  • Sufficient for 40 tests.
  • Can be used for marine, fresh and garden pond water

Salifert Oxygen Profi-Test Corals and marine fish require very high levels of oxygen concentration because of the low solubility of oxygen in salt water so it is very important to regularly test the level of oxygen present. The Salifert Oxygen Profi-Test is extremely fast, measuring oxygen levels in just a few minutes and is scaled from 2 – 14 mg/L. Sufficient for 40 tests. Can be used for marine, fresh and garden pond

A powerhead designed primarily to provide water circulation is a great choice for a backup source of aeration.  However, if you do a water change and lower the powerhead and forget to move it back up then it becomes useless as a source of aeration.  Water movement in the middle of the tank will not aerate the water.  Water motion and movement should be visible on the surface of the tank at all time.

Great Circulation is needed to prevent dead fish
Great Circulation is needed to prevent dead fish

Hydor Koralia Evolution Aquarium Circulation Pump

  • New and improved mount featuring vibration absorbing technology and magnetic suction cup with free positioning capabilities
  • Safe for use with wave-timers
  • Higher flow rates and lower energy consumption when compared to previous Koralia models.
  • Compact design
  • For use on saltwater or freshwater aquariums that need additional water circulation

In saltwater aquariums, a skimmer will provide a great third source of additional aeration.  In a freshwater (or saltwater) aquarium an inexpensive air pump connected to a bubbler will provide this function.

These bubble boxes are essential to prevent fish death during power outages:

Marine Metal Aerator Bubble Box

Marine Metal Aerator Bubble Box

  • Pumps 1.4 STL / minute
  • Designed for fresh and saltwater use
  • Space saver clam shell package 4″W x 7.5″Lx 2″D
  • Pumps 1.4 STL/minute
  • Designed for fresh and saltwater use
  • Space saver clam shell package 4″W x 7.5″Lx 2″D

Aerates up to 7-1/2 gallons. Runs up to 33 hours on 2 D cell batteries. Weighted airstone. Water resistant. 1.5 volt air pump.  Batteries not included.

Three sources of water movement and/or aeration will greatly reduce the chance of dead fish due to lack of oxygen in the tank.  Care should be taken to ensure all are working properly at all times.  In a small tank with just a few inexpensive fish, you can get by with two but for larger systems we would consider three the minimum.  A battery powered aerator is important to keep handy in the event of a power outage that lasts more than just a couple of hours.  A quick visual check of all systems before you go to bed at night can help prevent a disaster when you wake up the next morning.  Many fish sleep on the bottom of the tank where the oxygen will be the lowest in the event of a failure and if the oxygen dips too low they might never wake up.

Dead Fish -Temperature

Low Oxygen isn’t the only possible cause of dead fish.  A dramatic temperature fluctuation or pH fluctuation is also possible.  Typically these can be avoided with regular monitoring of the aquarium system and are unlikely to occur as fast as a tank crash due to a lack of aeration.

Tank Crashes can occur due to temperature fluctuations.  If the temperature rises over 82 or dips below 68 degrees then loss of life can occur for many fish species.  This can happen in a hot house without air conditioning.  It can also occur due to a faulty tank heater.  An inexpensive thermometer that is checked regularly will help you gauge the effectiveness of the tank heater as well as the effect of the temperature of your home on your tank.  Also, learn how the water feels when it is at the correct temperature.  When you feed or do routine maintenance you will be able to tell if the temperature of the water needs attention.  When you first buy a new water heater make sure you check it initially as there are occasional reports of an aquarium heaters thermostat not working properly and over heating.  Also, keep in mind that they can quit heating and do periodically need to be replaced.

Exo Terra Liquid Crystal Thermometer
Help prevent dead fish with a cheap Thermometer

 

The Exo Terra Liquid Crystal Thermometer is easy to read and install and can be placed inside or outside the terrarium. The Exo Terra Liquid Crystal Thermometer has a temperature range from 69-105 degrees Fahrenheit. Maintaining the proper temperature and humidity levels in a terrarium is vital for the well-being and health of all reptiles and amphibians. Exo Terra has developed a complete line of terrarium accessories, including the Exo Terra Liquid Crystal Thermometer that will help you monitor and maintain proper temperature and humidity levels for tropical, rainforest and desert environment.

Dead Fish -Ammonia

An ammonia spike can also cause a tank crash with multiple dead fish.  This is of course a great danger when initially cycling the aquarium but can occur after the initial cycling.  If you understand why it can occur after the initial cycle then you can be prepared and avoid it.  In lightly and even moderately stocked tanks there will typically be enough bacteria in the aquarium systems to handle occasional ammonia fluctuations even without any other biofiltration.  Even just a little biofiltration such as a biowheel will be more than enough to handle even significant ammonia fluctuations in these tanks.  Ammonia fluctuations can occur when adding fish to the system or when a fish dies and decomposes without you realizing it.  However, if you greatly increase the number of fish in the system at once or several fish die at once and there is no biofiltration in the system then it is possible to have an ammonia spike which can subsequently crash the entire tank.  It is a good idea to have ammonia test strips handy as well as ammonia neutralizing water conditioner around at all times specifically so you can monitor and neutralize any potential dangerous situations.  In heavily stocked aquariums this possibility is increased and you should be on the look out for any dead fish and try to remove them from the system as soon as possible.  Also, in heavily stocked systems, additional biofiltration such as a biological filter pad or biowheel is a necessary component.  However,  this can create a sterile system with chronically high nitrates.

An ammonia neutralizer should always be kept on hand in the event of an ammonia spike that can be caused by a dead fish, leading to more fish death.

Kordon AmQuel Plus $8.00
Kordon AmQuel Plus – Buy Here!

This aquarium essential is a Unique Water Conditioner Providing Actions Needed For Safe aquarium and Pond Keeping For Fishes and Invertebrates.
Nontoxic and Saves On The Need For As Many Water Changes As Would Otherwise Be Required.
Removes/Detoxifies All Of The Kinds Of Toxic Nitrogen Compounds In The Water.
Removes/Detoxifies All Forms Of Ammonia/Ammonium/Nitrites/Nitrates From The Water, Including Ammonia In Chloramines.
Is Safe To Use With Other Water Conditioners and Organic Herbal Fish Medications.

API Ammonia Test Kit for Aquarium

API Ammonia Test Kit for Aquarium

Ammonia tests are critical in a new tank to prevent dead fish.  

  • Contains one (1) API AMMONIA 130-Test Freshwater and Saltwater Aquarium Water Test Kit, including 2 bottles of testing solution, 2 color cards and 1 glass test tube with cap
  • Monitors water quality and prevents invisible water problems that can be harmful to fish
  • Monitors water quality and prevents invisible water problems that can be harmful to fish
  • Works instantly to make aquarium water safe for fish
  • Dose several times a week when starting a new aquarium then weekly or when problem arise

Dead Fish -pH

Multiple fish deaths are also possible due to a dramatic pH fluctuation.  This will not happen overnight but over a few weeks.  In neutral pH freshwater tanks a quick test strip test is adequate to make sure the tank pH is not dropping or rising to far too fast.  Generally a range between 6.5 and 7.5 will be fine for most freshwater fish.  For saltwater or high pH freshwater tanks the pH is a little harder to monitor with test strips and we recommend using a high range pH test kit and monitoring the tank weekly.  The pH in a high pH tank will naturally drop over time (unlike in a neutral pH tank) and you will sometimes need to add baking soda or other buffering additives to maintain the pH.   In saltwater aquariums the API high range pH kit is an essential tool to have.  At 8.0 the test will appear a light brown and at 8.4 the test will appear to be a purple.  You will want to monitor weekly … when it is a light brown you will add buffer until the test appears a light purple.  Otherwise a quick and dramatic fluctuation will not occur and you can easily prevent dead fish caused by inadequate pH.

API High Range pH Test Kit
API High Range pH Test Kit

API High Range pH Test Kit

  • Contains one (1) API HIGH RANGE PH TEST KIT 160-Test Freshwater and Saltwater Aquarium Water Test Kit, including 1 bottle of testing solution, 1 color card and 1 glass test tube with cap
  • Helps monitor pH and prevent invisible water problems that can be harmful to fish and cause fish loss
  • Accurately reads pH range 7.4 – 8.8, ideal for Goldfish, Marine, and African Cichlids.
  • Because different geographies have different tap water conditions, and different fish need different pH levels to be healthy, API helps measure pH levels & detect pH fluctuation caused by fish waste, uneaten food and addition of tap water.
  • Use for weekly monitoring and when water or fish problems appear

Dead Fish -Other Factors

There are other factors that will not crash a tank but can gradually kill organisms in the tank and reduce the overall quality of the aquarium system.

For coral and planted tanks proper lighting is necessary.  In coral tanks, maintaining proper calcium levels and other trace element levels in the tank is necessary.  In planted tanks, calcium is not an issue but having an appropriate substrate or occasional use of trace element fertilizer is important.  Failure to do so can result in the death of plants and corals.  Some other invertebrates will also require a proper balance of trace elements.  The use of quality trace element supplements and water changes, occasional water changes when denitrification is used, will ensure that the water quality remains high for all organisms.

Good water flow is the most important thing you can do in a cycled tank to prevent dead fish.

Ideally, an aquarium system will be as close to a healthy natural water ecosystem as possible.  A healthy natural system will have a healthy microfauna system with rotifers and copepods and even some organic molecules, negligible nitrates, plenty of oxygen, low phosphates, good water movement, and the proper levels of all trace elements.  pH, Salinity, temperature, overall hardness, and to some extent the type of trace elements needed (such as calcium) are really the only species specific variables.  Of those, oxygen absolutely is the most important factor to keep fish alive.  Salinity once established is pretty easy to maintain.  pH and hardness is important but fluctuates slowly and in neutral tanks fluctuates very slowly if at all.  Temperature is important but usually fluctuates little or slowly (except when a heater malfunctions) and fish can handle a fair range.  Nitrates are an issue, especially without denitrification, and are a major focus of aquarium systems … but typically will not cause multiple dead fish but instead just cause chronic problems and increase chance of fish disease, algae issues, and other long term problems in the aquarium.  Ammonia is a huge danger initially but after the initial cycle can generally be addressed without much problem.   Phosphates, calcium levels, and other trace elements are not typically a major problem but do need to be considered over the long term in order to maintain a well balances and healthy natural aquatic ecosystem.  Microfauna are definitely beneficial to maintain, especially in reef tanks or aquariums with any filter feeders … however some fish only systems can even function well without them at all.