Why you must support water, filtration, and fish now
The days are getting shorter. The nights are turning cooler. The first leaves are sometimes already falling into the pond.
For many owners, autumn really begins when it’s time to stretch out a net or stop feeding the fish. Yet, pond preparation begins well before the first cold days.
At this time, the water still bears the traces of summer: food distributed over several months, high fish activity, dust, pollen, fine organic matter, and heat waves. At the same time, the gradual drop in temperature begins to change the behavior of the koi and the biological activity of the filter.
There is, therefore, a short period that is particularly interesting: the water is still sufficiently active, but autumn has not yet set in.
At Aquiflor, we like to call this the preparation window.
The pond's spring is prepared in autumn
A pond does not become unbalanced overnight. Problems visible when the nice weather returns often have part of their origin several months earlier.
Leaves and plant debris that remain in the water are gradually decomposed by microorganisms. This transformation consumes oxygen and releases nutrients back into circulation. A study relayed by the USGS notably showed, in the context of urban waters, the considerable importance that leaves can have in seasonal phosphorus inputs.
In a garden pond, not all leaves obviously cause a catastrophe. But their accumulation, combined with food residues and fish waste, increases the organic load that the ecosystem will have to process during a period when its functioning is slowing down.
The best strategy is therefore not to treat more once the problem appears. It is to reduce now what the pond will have to manage later.
What does the drop in temperature really change?
Koi are ectothermic animals: their body temperature and activity depend directly on the water temperature. Research conducted on koi carp confirms that temperature variations clearly influence their activity and behavior.
Temperature also acts on the filter's microorganisms. Nitrification — the transformation of ammonium and then nitrites — is a biological process sensitive to environmental conditions, including temperature. When the water cools, its efficiency does not disappear abruptly, but it evolves and can slow down.
It is for this reason that the end of summer and the beginning of autumn should not be considered an "end of season." It is a transition during which two mistakes must be avoided:
-
continuing to feed exactly as in mid-summer even as fish activity decreases;
-
cleaning the filter too aggressively and destroying part of the biofilm at a time when its recolonization becomes slower.
The right "boost" is not a stimulant
When we talk about giving the pond a boost before autumn, it is not a matter of artificially forcing the fish or the bacteria.
Good autumn support consists rather of offering the pond better conditions before the water cools further: fewer fine particles, less unnecessary organic matter, preserved filtration, and water that is properly mineralized and sufficiently oxygenated.
In other words, we are not asking nature to work faster. We are making its work easier.
It is precisely with this logic that clay rich in montmorillonite, such as Aquipond BactoClay, can find its place.
Why add montmorillonite before autumn?
Montmorillonite has a microscopic layered structure and a large surface area for exchange. In water, it can interact with extremely fine particles, certain ions, organic matter, and microorganisms.
Its benefit before autumn is based on several complementary mechanisms.
1. Grouping together particles that the filter has difficulty retaining
Certain materials remain continuously in suspension because they are too fine to be captured effectively. Clay that is properly dispersed can promote their grouping into aggregates that are easier to retain through mechanical filtration.
The water may become cloudy temporarily after addition: this mineral veil is normal. It corresponds to the dispersion of the clay in the pond before it is gradually captured along with the associated particles.
2. Offering mineral surfaces to the biofilm
Montmorillonite particles can serve as adhesion substrates for certain microorganisms. Studies have observed interactions between this clay and bacteria, as well as an influence on biofilm formation for certain species.
This does not mean that the clay creates a universal "shell" around all good bacteria. The scientifically accurate formulation is more interesting: it can provide mineral surfaces on which part of the microbial life organizes itself.
3. Putting minerals back at the heart of an artificial pond
A pond with a liner or masonry exchanges much less with the ground than a natural pond. Adding mineral clay amounts to punctually reintroducing this link between the water and minerals.
This is not a measurable and identical remineralization in every pond: the result depends on the composition of the water and the clay. But this mineral dimension contributes to a more complete approach to the biotope.
And for the fish? Let's be precise
Cleaner, properly oxygenated, and biologically stable water creates a more favorable environment for fish as the cold season approaches. It is this indirect action that seems most sound to us.
There is research in aquaculture on montmorillonite administered in the feed of certain species, with observations focusing on growth, nutrient utilization, or certain physiological markers. But these studies do not allow us to claim that clay added to pond water "directly strengthens the immunity" of all koi.
At Aquiflor, we therefore prefer to speak of support for the fish's environment, rather than a medical promise.
Better-prepared water does not make a koi invincible. It simply spares it from some unnecessary stress at the time when its metabolism begins to slow down.
Why choose BactoClay at this time?
Not all clays have the same origin, particle size, or composition. Their color is also not enough to determine their quality: a perfectly white clay is not automatically purer or more effective.
Aquipond BactoClay has a natural beige tint and contains 86% montmorillonite according to the product specifications. Its formulation was developed over more than two years with particular attention paid to three field realities:
-
good dispersion in water;
-
use in koi ponds and decorative ponds;
-
compatibility with modern filtration systems, especially drum filters.
We will not say that no clay can work properly in a drum filter. We can, however, explain why this criterion mattered from the very beginning of BactoClay's development: clay intended for modern ponds must support the filtration, not become an additional constraint when used correctly.
The Aquiflor routine for preparing the pond before autumn
BactoClay should not be used to mask a lack of maintenance. It makes the most sense as part of a coherent preparation.
1. Remove what should not decompose in the water
Regularly remove leaves, wilted flowers, plant debris, and easily accessible deposits. Install a net if the pond is surrounded by trees.
2. Check the water before correcting
Check at a minimum the pH, KH, GH, nitrites, and, if necessary, ammonia. Autumn rains can gradually dilute minerals and lower hardness levels.
Do not correct anything blindly. If your values are good, there is no reason to modify the balance.
3. Maintain filtration with moderation
Clean the mechanical parts that need it, but avoid stripping all biological media simultaneously. The filter biofilm constitutes a living heritage that must be preserved.
4. Gradually adapt feeding
Observe the fish and measure the water temperature. Gradually reduce quantities as their activity decreases and choose food adapted to the season.
5. Use BactoClay according to the manufacturer's dosage
Distribute the product correctly according to the instructions. An overdose does not improve the result and can unnecessarily stress the mechanical filtration. On a drum filter, simply monitor the rinse cycles after application, as with any mineral powder.
The best time is before you need it
Waiting until the water is cold, leaves have accumulated, and the fish are nearly inactive reduces the possibilities for intervention.
Preparing the pond now allows you to act gently while the ecosystem is still actively functioning. BactoClay is not a miracle autumn cure. It is a mineral tool that fits into a much more important approach: entering the cold season with the least organic debt and as much stability as possible.
That may, in the end, be the real boost: not pushing the pond to the limit, but giving it better foundations to navigate the transition.
Discover Aquipond BactoClay and how to use it →
[Insert direct link to product page here]
Do you not know your water values? Bring a sample to Aquiflor. Our experts will analyze it for free and advise you only on what your pond really needs.
References
-
Zhong G. and Ren Z. (2025), The Behavioral Responses of Koi Carp (Cyprinus carpio) to Different Temperatures. Animals. https://doi.org/10.3390/ani15070943
-
Kinyage J.P.H. and Pedersen L.-F. (2016), Impact of temperature on ammonium and nitrite removal rates in RAS moving bed biofilters. Aquacultural Engineering. https://doi.org/10.1016/j.aquaeng.2016.10.006
-
Sun Y. et al. (2023), Facilitated Adhesion of Bacteria on the Na-Montmorillonite Surface by Ca²⁺. ACS Omega. https://doi.org/10.1021/acsomega.2c07260
-
Ma W. et al. (2017), Bacillus subtilis biofilm development in the presence of soil clay minerals and iron oxides. npj Biofilms and Microbiomes. https://www.nature.com/articles/s41522-017-0013-6
-
U.S. Geological Survey (2016), Removal of Fallen Leaves Can Improve Urban Water Quality. https://www.usgs.gov/news/state-news-release/removal-fallen-leaves-can-improve-urban-water-quality
