Power outage and aquariums – how do canister filters react without electricity?
For the second time this year, a major summer storm caused a prolonged power outage. Fortunately, living in a rural home, I’ve equipped myself with a generator that provides backup power for key devices in my aquariums. Among aquarists, there’s a widespread belief that biological filters, reliant on aerobic microorganisms to purify water, are particularly vulnerable in such situations.
Canister filter in an aquarium – What happens during a water flow interruption?
Canister filters filled with materials like sponges or ceramics, serving as substrates for beneficial microorganisms, are now standard biological filtration systems in medium-sized freshwater aquariums. During an unexpected power outage, pumps stop, halting the flow of oxygen-rich water that provides sustenance for the bacteria cleaning the water.
How long can a canister filter survive without power? Key questions
It’s often claimed that within an hour, the oxygen levels inside the filter can drop to critically low levels. Backup power solutions like generators or battery-based systems are arguably the best options to keep the filter operational in such emergencies. But what if you lack an alternative power source? How long can a canister filter last without water flow? Is it really just an hour? Is there anything we can do to prolong the survival of the bacteria?
Experiment: The impact of power outages on aquarium filters
Together with a friend and co-creator of the aquaristic YouTube channel “Underwater Worlds Aqua Test”, we decided to tackle this topic in one of our episodes. Inspired by real events and having access to a professional laboratory-grade oxygen meter, we conducted a simple experiment.
The oxygen meter, equipped with a probe resembling that of a pH meter, measures dissolved oxygen levels. This particular model also allows automated data logging at set intervals—perfect for placing the probe inside a ceramic-filled filter, shutting off the power, and recording the results.
Why is oxygen in a biological filter so important?
To interpret the results, we need to understand how much oxygen bacteria require to function. Aerobic bacteria used for water purification need a minimum oxygen level of about 2 mg/L. Below this threshold, their metabolic processes slow down, reducing their efficiency in cleaning the water. At critical levels of 0.5 mg/L or less, bacterial activity nearly ceases.
The experiment aimed to determine how quickly the oxygen level in the filter drops first to 2 mg/L—where bacterial activity slows—and then to the critical level of 1 mg/L, which we defined as a safety margin.
Experiment procedure: testing the impact of power interruption on filters
For this experiment, we used a year-old 300L planted aquarium with two canister filters filled with mixed ceramic media. The tank, featuring strong lighting and CO₂ injection, supports intense photosynthesis. Prior measurements showed that oxygen levels in the tank fluctuate daily from 5 to 9 mg/L, depending on the lighting cycle.
We prepared a filter with an oxygen probe inserted through a specially drilled hole, filled it with ceramic media from a working filter, and operated it for several days at a flow rate of 600 L/h.
Before shutting off the filter, we noted that oxygen levels inside the filter were typically 1 mg/L lower than in the aquarium, fluctuating between 4 and 8 mg/L. Depending on the time of day, the initial oxygen levels at the time of the power outage varied significantly, prompting us to conduct two experiments: one at peak oxygen levels and another at the lowest.
Experiment results: How long until the filter runs out of oxygen?
In both scenarios, oxygen levels dropped sharply right after the filter stopped, likely due to the absence of fresh, oxygenated water. After stabilization, oxygen levels declined steadily at a rate of about 1 mg/L every 2.5 hours until reaching 2 mg/L.
- In the first experiment, this threshold was reached after 10 hours.
- In the second, it took just 2 hours and 45 minutes.
The critical level of 1 mg/L was reached in:
- 12 hours and 45 minutes in the first test,
- 5 hours and 20 minutes in the second.
Can opening the filter help during a power outage?
In the first experiment, after over 24 hours without flow, when oxygen levels were below 0.5 mg/L, we opened the filter to allow natural gas exchange. Within minutes, oxygen levels rose to around 2 mg/L, indicating that such a simple action could reinitiate bacterial activity temporarily.
Practical tips for handling aquarium power outages
While one experiment cannot provide definitive answers, it aligns with general knowledge. For aquariums relying on photosynthesis for oxygenation, the time of a power outage significantly impacts the filter’s survival.
Key takeaways include:
- Maintain High Oxygen Levels: Ensure good oxygenation in your tank, especially during the day.
- Clean Filters Regularly: Dirty filters deplete oxygen faster.
- Open Filters During Outages: If no backup power is available, opening the filter can extend its viability.
Will the filter’s bacteria survive without oxygen?
Does a critical drop in oxygen levels mean immediate death for aerobic bacteria? Not necessarily. Some bacteria form spores to endure adverse conditions, while facultative bacteria can switch to alternative metabolic processes, such as using nitrates instead of oxygen.
Thus, a temporary drop in oxygen may not mean the end of your biological filter, but prolonged deprivation will lead to deterioration over time.
This article was created in collaboration with the “Podwodne Światy Aqua Test” channel, where you can watch the full experiment.
