Aquarium Crash: The Delicate Balance

bacterial bloom

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Experienced aquarists understand that maintaining a healthy aquarium is akin to conducting a delicate symphony. The equilibrium between living organisms and their aquatic environment must be finely tuned for a thriving ecosystem. However, unforeseen disruptions can turn this harmonious ensemble into a cacophony of chaos, leading to an aquarium crash—a dreaded nightmare for any aquarium enthusiast.

Acidity Creeping In: The Buffering Capacity Challenge

At the heart of aquarium keeping lies the nitrogen cycle, a biological process whereby bacteria converts toxic ammonia into less toxic nitrate. Fish and other inhabitants produce ammonia (NH3) and ammonium (NH4) as waste products, setting the stage for nitrifying bacteria to convert those waste products into nitrite (NO2) and further into significantly less toxic nitrate (NO3). This continuous cycle ensures the aquarium environment doesn’t become oversaturated with dangerous ammonia or nitrite, and is the key to a stable and functioning aquatic environment.

As the nitrogen cycle progresses, it leaves behind a hidden danger—acidity. The process releases hydrogen ions (H+), slowly eroding the aquarium’s buffering capacity. Like sands through the hourglass, so goes the buffering capacity in our aquariums. I’ve used a seesaw analogy with pH before, and in a closed system you have to envision the kid on the acid side of the seesaw getting forever heavier until ultimately that side is resting directly on the ground. This is what happens when a tank goes into a “crash” mode: the acidity has developed to such a significant degree that the buffering is incapable of boasting the pH, resulting in a pH drop to levels that are very potentially unsafe for aquarium life.

Low pH: An Impediment to the Nitrogen Cycle

Research has demonstrated that the type of bacteria that neutralize ammonia are impacted by pH with, and most research indicates that nitrification reaches its peak rate  at a pH of about 8.0-8.25, which is why Fish Geeks recommends a pH of neutral or slightly alkaline for most freshwater aquariums. However, at low pH levels, the nitrogen cycle encounters an impasse as a pH below 6.5 has been demonstrated to slow the rate of nitrification. As pH reaches around 5.0, the cycle grinds to a halt, obstructing the transformation of nitrite into nitrate. The end result—ammonia may accumulate in the aquarium, posing a toxic threat to its inhabitants.

As the pH levels decrease, an intriguing tug of war ensues between ammonium (NH4) and its toxic gaseous counterpart, ammonia (NH3). At lower pH, the equilibrium leans towards the safer ammonium form, creating a quixotic situation where the very cause of the ammonia spike—low pH—is also a factor that mitigates its potential deadliness. However, a hasty response, such as dosing alkaline buffer, could disrupt this delicate balance, pushing the equilibrium towards ammonia toxicity. Achieving stability requires a more nuanced approach.

Signs of Aquarium Crash: Bacterial Blooms and Fish Distress

There are often visual cues of an aquarium experiencing a pH crash, notably bacterial blooms take center stage, casting an ominous hue over the once-pristine environment. The increased availability of ammonia in the water serves as a rich food source for the nitrifying bacteria, triggering their rapid reproduction. The bacterial population multiplies exponentially, forming visible colonies or clouds in the water. As a consequence, the water may become cloudy or appear milky white, giving the appearance of a foggy day within the aquarium.

While the bacterial bloom itself is not harmful to fish or other aquatic life, it indicates an imbalance in the aquarium’s nitrogen cycle. Bacterial blooms are common in new aquariums and are often part of what we like to call “new tank syndrome,” however, blooms can also mean a serious disturbance in the aquarium environment. If you have a bloom, consider recent aquarium product doses including buffer or bacterial compounds. If no recent changes have been made, it is prudent to do your system a complete once-over to determine if the disturbance is due to improper chemical parameters, malfunctioning equipment, or potential power failure.

Meanwhile, our beloved fish endure the brunt of the calamity. Ammonia poisoning wreaks havoc on their sensitive gill structures, leading to inflammation and distress. Fish may seek refuge near the water surface or rest lethargically on the substrate, displaying signs of heavy breathing. Nitrite poisoning manifests similar symptoms, with unnatural coloration sometimes evident in the gills.

If you confirm that a nitrite spike is causing your fish distress adding aquarium salt at the rate of 3 grams of salt per liter of aquarium water can help alleviate this stress by altering osmoregulation, preventing excess nitrate from being assimilated into the fish. Both ammonia and nitrite spikes can also be effectively mitigated (at least in the short term) by the addition of a product like Seachem Prime, which will rapidly (and temporarily) detoxify these compounds the aquarium.

Once the bacterial population reaches a sufficient level to handle the ammonia load, the bloom will naturally subside, and water clarity will improve. If you’re not establishing a new aquarium, water changes are a prudent option for improving water quality. You can also choose to employ a flocculant  to help clear the aquarium. A flocculant is a chemical that helps increase water clarity by binding fine particles together, forming larger clumps that are easier for the filter to capture.

The Solution to Pollution is Dilution

When faced with excess toxic nitrite (NO2) and ammonia (NH3/NH4) in the aquarium, water changes are a highly effective and immediate solution. Water changes involve removing a portion of the aquarium water and replacing it with fresh, clean water. This process helps dilute the concentration of harmful compounds, reducing the stress on aquatic inhabitants.

To deal with an aquarium experiencing a pH crash and ammonia/nitrite spike, follow these steps:

      • Test water parameters: Before conducting a water change, test the aquarium water temperature to confirm the functionality of your heating element. Next test for nitrite and ammonia levels as well as the pH and alkalinity (KH). This will provide crucial information on the severity of the issue and guide the necessary actions.

      • Perform a partial water change: The size of the change depends on multiple factors, including your experience as an aquarist. If your tap water is known to have chloramines, it may be prudent to employ reconstituted RO water.

      • Use a water conditioner: When adding fresh water during water changes, always use a dechlorinator to neutralize harmful chlorine and chloramines present in tap water. Chlorine can stress and harm fish, exacerbating the existing issue. Some water conditioners, like Seachem Prime, also help detoxify ammonia and nitrite, providing an additional layer of protection for aquarium inhabitants during this critical period.

      • Repeat: You may need multiple water changes, a python water changer system is a great way to reduce the workload of each change. After each water change, monitor water parameters to track the reduction of nitrite and ammonia levels. Regular testing will help ensure that the water changes are effectively addressing the issue.

      • Address the underlying cause: Test your source water for its alkalinity/KH level to ensure it has adequate buffering capacity. If the value is not near 10dKH, you should keep a careful eye on your aquarium alkalinity and pH values.

    Lastly, be patient and consistent. Dealing with excess nitrite and ammonia requires time and diligence. It may take several water changes and consistent monitoring to fully resolve the issue. Be patient and continue with proactive maintenance practices.

    Prevention: The Elixir of Regular Water Changes

    An ounce of prevention is worth a pound of cure, as the adage goes. Embrace the practice of regular water changes, which have always been and will always be your best bet for avoiding impending disasters. By exporting excess acids from the aquarium, you prevent crises in their infancy. In marine setups where water changes represent a larger logistical hurdle, diligent monitoring of alkalinity and judicious dosing of alkaline buffers helps maintain this equilibrium.

    Last Word

    It is crucial to recognize that acids are constantly accumulating in your aquarium, and thus so is the buffering capacity of your aquarium water. This gradual but inevitable process can lead to a pH crash, which, in turn, may trigger ammonia spikes, posing a serious threat to aquatic life. Understanding that the solution is the institution of regular water changes rather than attempting a pH increase by itself. By addressing the issue proactively, you can maintain a stable and thriving aquarium for your aquatic companions.


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