Problems with the Nitrogen Cycle

Ammonia, Nitrites and Nitrates measure the biological filter in a system.  Elevations in any of these parameters with normal pH and alkalinity indicates a problems with biological filtration (see related article: The Importance of Water Quality Testing on this website).  Mild elevations in all parameters are generally easy to fix, but there are some special cases described below that are far more concerning.

Mild elevations in all three parameters together generally indicate too much bioload in the system.  The most common causes are excess feeding and too many fish in the aquarium.  Food, feces and other biological material break down to ammonia and are converted to nitrites and nitrates by the bacteria in the biological filter.

Mild Elevations in All Nitrogen Cycle Parameters

Immediate steps:

1. Perform a 30-50% water change
2. Discontinue feeding until the filtration problems have been corrected

Other important steps:

1. Evaluate feeding:  You should only feed what will be eaten in 2 minutes.  Overfeeding is the most common cause of biological filtration problems.  Correction of overfeeding may be all that is needed for a long term solution
2. Look at the number of animals in the tank.  Too many animals means too much waste.  Overcrowding is the second most common cause of biological filtration problems. It can also cause stress and aggression.  If the tank is overcrowded, it may be time for a second aquarium, or upgrade to a larger aquarium.
3. Evaluate the filter.  If feeding is appropriate and the tank is not overcrowded, then the problem most likely lies in the filter.  The biological filter is bacteria.  The bacteria grown on a wheel, brushes, live rock or bio-balls depending on the system.  More surface area may need to be added.  Reptiles, amphibians and meat eating fish such as Lionfish require far more filtration than other systems.  Alternatively there may be enough surface area, but the bacteria may have been damaged by medications, chemicals or temperature fluctuations in the aquarium.  This can be corrected with time and the addition of bacteria from another established system.  Until the biofilter is back to normal on water quality parameters, water changes will need to be done every 24-48 hours to keep ammonia levels down.

“New Tank Sydrome:” High Ammonia, Zero Nitrites and Nitrates

As the name implies, this may be a new system that was not properly cycled before adding fish (see Cycling a Tank on this website), or the bacteria in the biological filter may have been killed by chemicals, medications or temperature fluctuations.  This is a primary reason to avoid adding medications without the advice of a veterinarian experienced with exotic animals.

Immediate steps:

1. Perform a 50% water change

Other important steps:

1. Evaluate the biological filter as above (#3 of other important steps for Mild Elevations in All Nitrogen Cycle Parameters)
2. The animals in the system should be evaluated by a veterinarian experienced with aquatic animals.  High ammonia levels can do damage to the gills and result in health problems that can be fatal even after the water is corrected. 
3. If possible the animals should be moved to a cycled tank until the water quality is corrected and the biological filter is back to normal.

“Old Tank Syndrome,” or “pH Crash:” Low pH, Low Alkalinity, High Ammonia

This situation appears as a sudden crisis, but it is the result of a long-standing problem.  Alkalinity is a measure of buffering capacity; in other words, the ability for pH to remain stable in an aquarium or pond.  Old Tank Syndrome results from chronically low alkalinity.  When the alkalinity finally gets too low to keep the system stable, the pH drops rapidly.  This drastic shift in pH usually results in deaths very quickly.  Preceding this, there may have been some deaths immediately after water changes.  A significant amount of work is required to correct this problem. 

Immediate and other important steps:

1. Add ammonia locking products (Ammonex, activated charcoal, etc.)
2. DO NOT change water immediately.  Another rapid change in pH could result in more deaths.
3. Try to locate an established aquarium and transfer surviving fish with a slow acclimation.  Animals remaining in the aquarium have greatly increased risk of mortality.
4. If it is not possible to relocate the inhabitants of the system, then buffering agents should be added before a water change.  SLOWLY add sodium bicarbonate (baking soda) to stabilize the pH.  When alkalinity is reading over 50ppm, then water changes can be started.  The alkalinity of added water should be checked for water changes and should be similar to tank water to avoid further fluctuations. 
5. The surviving animals should see a veterinarian familiar with aquatic animals.  pH changes can cause long term health problems and immediate damage to the gills.
6. Watch for New Tank Syndrome as the system is stabilized.  The pH change can also damage the biological filter.
7. After the tank is stabilized, alkalinity needs to be corrected long term.  Sodium bicarbonate should be considered a short term solution.  See alkalinity problems below.

Temperature problems

Most aquatic animals are ectothermic or poikilothermic, meaning they do not control their own body temperature.  Changes in water temperature can affect their normal body functions.

Elevated temperature:

Temperature elevations can occur from failure of an air conditioner in the home, placing the aquarium too close to a heat source, improper shading for a pond or from a failure in the thermostat in the heater.  Heat stress is more serious for fish than hypothermia. 
Immediate steps:

1. Return the temperature to normal as quickly as possible.  Float ice packs in the water or change aquarium water with cooler water.
2. Aerate the water immediately.  The warmer the water, the less oxygen it can hold.  Adding air stones or agitating the water improves the chances for survival.
3. Unplug heaters in the system.  DO SO CAREFULLY.  There may be a short in the heater.  The heater should be plugged into a circuit with a breaker that can be turned off prior to handling the plug.

Other important steps:

1. Stop feeding for 2-3 days, then start feeding again slowly.  The bacteria in the biological filter may have also been damaged.  (see Nitrogen Cycle section in this article)
2. Consult a veterinarian familiar with aquatic animals.  Heat stress can suppress the immune system of the fish and lead to secondary health issues even days after the heat stress incident.
3. Replace the tank’s heater.  Look at the wattage of the heater.  The proper wattage is 5-10 Watts per gallon.  This may be the source of the problem.  Even if Wattage is correct, the heater should be tested or replaced because the safety devices may be failing.

Low Temperature

This is usually related to placement of an aquarium near a window or air conditioning vent, heater failure or the use of a heater with lower wattage than needed for the system.
Immediate steps:

1. Remove, inspect and if necessary, replace any heater from the system.  Do this carefully by turning off power to the outlet before unplugging the heater.
2. Float bags of warm water in the aquarium to SLOWLY raise the temperature to normal.  Increasing the temperature should be done at a rate of 1-2 degrees Fahrenheit per hour.

Hypoxia (Low Dissolved Oxygen)

Suspect this with any sudden loss of fish or upon seeing fish gulping for air at the surface.  With aquariums, this will usually result from electrical failure causing pump failure.  In ponds, several overcast days can reduce photosynthesis from plants and algae that produce oxygen.  Overcrowded ponds may also have low dissolved oxygen in the morning when photosynthesis has stopped overnight.  The sudden death of algae in a system can also lead to a rapid oxygen depletion and increase in ammonia simultaneously.  This is the hidden danger of using chemical treatments to eliminate algae rather than addressing husbandry.

Immediate steps:

1. Increase oxygenation with surface agitation, air stones or both. 
2. Lower the water temperature.  Adjusting the temperature down by 5 degrees Fahrenheit will increase the water’s capacity to hold oxygen.

Other important steps:

1. Inspect and replace pumps if needed.
2. Evaluate the number of animals in the system.  Overcrowding is often an underlying problem that needs to be corrected. 
3. If there is excess algae in a system, correct it with proper filtration and husbandry.  Algaecidal chemicals can cause too drastic a change in the system. 

Low Alkalinity with normal pH, ammonia, nitrites and nitrates

Alkalinity is important as a buffering system.  Low alkalinity is normal for some Amazon River species where pH is maintained at a low level with the addition of CO2 but higher alkalinity is needed in most systems.  Poor control of Alkalinity can lead to a sudden change that will become fatal for animals in the system (see Old Tank Syndrome above).

Immediate steps:

1. If alkalinity is low, test calcium.  The combination of the two values helps determine the best way to correct low alkalinity.
2. If calcium is normal to high with low alkalinity (#4 on the diagram), then add sodium bicarbonate or sodium carbonate.  Be careful not to use anything with perfumes or surfactants.  If calcium and alkalinity are both low (#2 in the diagram), then add a balanced solution like B-ionic or C-balance. 
3. If you have attempted the steps in number 2 and alkalinity remains low, check magnesium levels and correct any deficiencies.

Other important steps:

1. In fresh water, addition of limestone (calcite or dolomite) will help stabilize the alkalinity and calcium levels in the longer term.
2. In salt water, add crushed coral or add a Kalkwasser reactor to the system if repeated problems are encountered.  Alternatively, search for another water source or a different salt.

References for further knowledge:
1. Marine Chemistry: A Complete Guide to Water Chemistry in Marine Aquariums, by C.R. Brightwell.
2. The Reef Aquarium: A Comprehensive Guide to the Identification and Care of Tropical Marine Invertibrates, by Charles Delbeek and Julian Sprung.
3. Aquarium Corals: Selection, Husbandry and Natural History, by Eric H. Borneman.
4. http://www.advancedaquarist.com/2002/11/chemistry