When a pond owner applies coccolithic chalk (CaCO₃) to remineralize their water, they generally expect to see their pond become more balanced... not browner. However, this reaction is regularly observed with certain products.
The good news is that, in the majority of cases, this does not mean the pond is in danger. It primarily reveals a difference in quality between the various types of chalk available on the market.
What is coccolithic chalk?
Coccolithic chalk is a natural sedimentary rock consisting mainly of calcium carbonate (CaCO₃).
It comes from the accumulation of billions of fossilized marine micro-algae called coccolithophores, which left behind their tiny calcareous plates. These deposits formed over millions of years.
Thanks to this composition, coccolithic chalk is used to:
- increase GH and KH;
- stabilize the pH;
- improve the water's buffering capacity;
- stimulate bacterial life;
- promote a healthier environment for fish and plants.
Not all coccolithic chalk is equal
This is probably the most important point. Two bags labeled "Coccolithic chalk" or "CaCO₃" can offer very different results.
The differences specifically concern:
- the purity of the calcium carbonate;
- the particle size;
- the fineness of the grind;
- the potential presence of mineral impurities;
- the ease of dispersion in water.
Coarser or less homogeneous chalk may remain in suspension for a long time or cause fine particles already present at the bottom of the pond to be stirred up.
The result is water that temporarily takes on a beige, light brown, or brown tint.
Why does the water turn brown?
Several phenomena can explain this coloration.
1. The particles remain in suspension
The finest particles scatter light and give the impression of cloudy water.
Depending on their grain size, it can take anywhere from a few hours to several days for them to settle.
2. Circulation stirs up sediments
Applying the chalk or strong water circulation can put organic deposits present at the bottom of the pond back into suspension.
The water then takes on a brownish tint that gradually disappears with settling and filtration.
3. Product quality
This is often the most decisive factor.
A very fine and pure chalk distributes much more evenly in the water than a product containing more coarse particles or impurities.
Why Aquiflor has chosen only Nautex
After testing numerous solutions over the years, we have made the choice to offer only one type of coccolithic chalk: Nautex.
Its main advantages are:
- very high purity;
- exceptional fineness of grind;
- homogeneous dispersion in water;
- rapid action on the mineral balance;
- a greatly reduced risk of prolonged water discoloration.
This quality explains why Nautex is widely used for ponds, natural pools, and ecological restoration projects where precise dosing is essential.
How long does it take for the water to become clear again?
In the majority of cases:
- a few hours with efficient filtration;
- 24 to 72 hours in a standard pond;
- a little longer in a natural pond without filtration.
If the discoloration persists for more than a week, it is advisable to check:
- the dosage applied;
- the quality of the chalk used;
- the potential presence of silt or organic matter being stirred up.
If your water has turned brown after adding coccolithic chalk, there is no need to panic. In most cases, this is a temporary phenomenon linked to the suspension of fine particles or sediments.
However, this situation serves as a reminder that there are major quality differences between the coccolithic chalks available on the market. Their origin, purity, and fineness of grind directly influence how they behave in the water.
It is precisely for this reason that Aquiflor has chosen to distribute exclusively Nautex, a coccolithic chalk recognized for its quality, purity, and excellent fineness, in order to offer a result that is as effective as it is clean when remineralizing ponds.
Complementing the action of the chalk with bacteria to restore clearer water
Adding high-quality coccolithic chalk like Nautex helps to rebalance water chemistry and provides an environment much more favorable to bacterial life. But to obtain clear water more quickly, it is often wise to supplement this treatment with a dose of specially selected bacteria.
Natural bacteria such as Aquipond Bactovase accelerate the breakdown of organic silt, dead leaves, leftover food, and decomposing matter that clouds the water and feeds algae. By consuming this organic matter, they gradually reduce the available nutrients, improve the biological quality of the pond, and promote clearer, more balanced water.
The combination of premium coccolithic chalk and bacterial inoculation constitutes one of the best strategies for sustainably restoring the balance of a natural pond. This is indeed the approach we recommend daily at Aquiflor after analyzing thousands of ponds: acting on both water parameters and its biological balance allows for much more lasting results than a single, isolated treatment.
