Once the winter operation mode has been decided, the filter no longer requires the exact same routine as in summer. Food quantities change, flow rates may need to be adjusted, and frost becomes a risk for certain parts of the circuit.
Managing filtration in winter consists of monitoring what circulates, what accumulates, and what the analyses reveal. This guide proposes a monitoring routine for an installation kept in service when its manual allows it, followed by points to follow if it has been winterized.
Start with an operation sheet
Note the reference for the pump, filter, and UV, as well as their winter status: in service, stopped, or dismantled. Add the path of the pipes and the location of important valves.
This sheet avoids misunderstandings if several people are involved. A pump that has been intentionally turned off must not be plugged back in while the circuit is drained. A valve opened for a specific operation must be clearly identified.
Keep the corresponding manuals. Some require a shutdown before frost or below a certain temperature. A monitoring routine does not allow for ignoring equipment usage limits.
Visual checks to be done regularly
Look first at the fish and the pond level, then at the water return. Does the flow resemble what was observed after the autumn preparation? A sudden drop can signal an obstruction or a pump problem.
Inspect accessible fittings and the areas around the filter. A new damp area, an unusual leak, or a different sound warrants investigation. Water can escape far from the pond if the circuit runs through a flower bed or a building.
During periods of frost or after a breakdown, perform checks more frequently. A return that is still flowing can gradually narrow due to ice. Do not consider the sound of the motor as sufficient proof of circulation.
Keep access paths clear from a stable area. Winter checks should be possible without walking on ice or dismantling hard-to-reach protection.
A short notebook is better than an impression
You can use five columns: date, water temperature, observed flow, analyses, and intervention. A few words are enough when everything is stable; describe changes in more detail.
| Monitoring point | What to note | Why it helps |
|---|---|---|
| Temperature | Measured value and trend | Connect activity and feeding to actual conditions. |
| Circulation | Normal, weak, or irregular return | Identify a hydraulic change. |
| Water | Results with units | Compare analyses over time. |
| Maintenance | Cleaned part and date | Understand what precedes an improvement or a difficulty. |
Avoid writing only "filter done." Specify if you emptied a basket, rinsed mechanical foam, or intervened on biological media. These operations do not have the same effect.
Mechanical filtration continues to trap waste
Koi feeding may be interrupted, but leaves and plant fragments can still enter the circuit. Check baskets and pre-filters according to the accumulation and the model's recommendations.
Do not let trapped waste accumulate under the pretext that the water is cold. Their presence can hinder water passage and increases the organic load to be managed in the installation.
Carry out targeted maintenance, then check the flow. On a filter with a dirty water outlet, check the final position of the control and its expected closure. An error after cleaning can lead to continuous water loss.
Also prepare the discharge of cleaning water so that it does not create a sheet of ice on a walkway. Practical organization counts especially when temperatures drop.
Preserve biological function when maintained
The filter's microorganisms depend notably on the circulating water, oxygen, and chemical conditions. Their activity evolves with temperature. It is not just a switch that turns off everywhere at the same degree.
Avoid harsh, simultaneous cleaning of all media in a filtration system that remains biologically active. Follow the manufacturer's method and use water suitable for the planned rinsing. Do not try to make every piece of media look new.
A filter can be clean on the outside and still treat the load insufficiently. Monitoring nitrites and ammonium is therefore more informative than the appearance of the foams alone.
Which analyses should be kept during winter?
Frequency must take into account the population and the stability of the pond. Regular monitoring remains relevant, with additional checks after a breakdown, a major intervention, or abnormal behavior.
Monitor temperature, pH, KH, and nitrogen compounds useful to the context. Note the GH in your general tracking without confusing it with the KH. A correction should be decided based on an interpretable measurement and an identified need.
The JBL ProAquaTest CombiSet Pond kit includes, among other things, pH, KH, GH, ammonium, and nitrites. Respect the conditions for use and storage of the reagents. Test equipment left in a room where it freezes may no longer be in the expected conditions.
If the fish are breathing with difficulty, routine analyses do not replace checking oxygenation. This kit does not measure dissolved oxygen.
Adjust the load: food and population
Reduce Koi feeding in line with their activity and the temperature, until stopping when conditions require it. Also respect the limits of the food being used. Remove any leftovers.
Sturgeons require distinct management since they continue to be fed in winter. In a mixed pond, the filter may therefore still receive a regular food load even if the Koi appear less active.
Do not add fish to "enjoy clear water" without re-evaluating conditions. Transparency does not describe available oxygen or the system's capacity to process an additional load.
What to do after a circulation failure?
Search for the cause and check the state of the circuit before restarting. A frozen pipe, an obstructed hose, or a damaged fitting must be treated before putting it back under pressure.
The duration of the shutdown, the temperature, and the filter load influence the state of the water and the media. There is no single deadline after which everything would be intact or lost. Do not automatically send stagnant, suspicious water back to the fish.
If the condition of the filter is uncertain, ask for a restarting method adapted to the model. Check the pond water and adapt feeding during the recovery. An improvement in flow alone does not confirm the restoration of biological capacity.
Should bacteria be added during winter?
An input should meet a need and adhere to the product's conditions of use. It does not compensate for a stopped circuit, a frozen pipe, or insufficient oxygen.
The Aquipond NitriBoost bacteria are offered particularly for seeding and recovery after certain interventions. The product sheet indicates an optimal water temperature above 10°C and a pH between 6.5 and 8 for their optimal functioning.
In colder water, do not make it an automatic routine. Instead, prepare for a coherent recovery when conditions are suitable. After an addition, continue analyses: the product does not constitute proof of an immediately established cycle.
If the filter has been winterized, what remains to be monitored?
Check storage and protection against frost. Parts must remain in the state required by their manual, either dry or in water depending on the component. A pump stored damp does not justify submerging its electrical plug.
At the pond, observe the fish, the air exchange, and the water level. Stopped filtration does not eliminate the needs of the population. If conditions deteriorate, the solution must be re-evaluated with appropriate advice.
Before spring, prepare the seals or parts to be replaced, reassemble according to the procedure, and check for leaks. The resumption of feeding will be progressive, following temperature and analyses.
Prepare a simple follow-up until spring
Gather equipment references, measurements, and the latest interventions. You will have a concrete basis for adjusting maintenance and organizing the restart.
See the pond analysis kit →
Consult the conditions for using NitriBoost →
Sources
- OATA — How to Look After Pond Fish: water, filtration, and seasonal feeding.
- Merck Veterinary Manual — Environmental Diseases of Aquatic Animals: biological functioning and environmental parameters.
- OASE — Preparing your pond for winter: protection and monitoring of circuits.
- OASE — FiltoClear 5000–31000 manual: example of maintenance and winterization specific to a range.
- Aquishop product sheets for JBL CombiSet Pond and Aquipond NitriBoost linked in the article: analyses included and conditions for use.
