Algae are almost never the real problem in your pond

If we had to summarize years of questions about algae at the Aquiflor counter, it would be this: almost everyone looks for the product that will make them disappear, and almost no one asks why they are there. It's understandable: algae are visible and bothersome, and a green pond is disheartening. Yet algae are a symptom, not a disease. They take advantage of an imbalance that existed before them: too much organic matter, a saturated filter, poorly circulating water, or a lack of oxygen. As long as we only treat the symptom, it comes back.

Why we target the wrong thing

The usual reasoning is simple: I see algae, so my problem is algae. It's a bit like treating a fever without looking for the infection. Algae are opportunistic organisms: they do not appear by chance, they occupy a space left vacant. In a balanced pond, nutrients are consumed by plants and bacteria, organic matter is broken down as it accumulates, and the water is oxygenated everywhere. There is little room left for them.

When the balance deteriorates, they are simply the first to show it because they react very quickly, within a few days, whereas plants take weeks.

Reading your algae as a diagnosis

Each type of algae tells a different story. Learning to read them can save a considerable amount of time.

Conversely, a light film of green algae on walls and stones, in clear water, is not a problem: it is a sign of a living pond, and it feeds a whole range of beneficial microfauna.

The five real problems behind algae

1. Accumulation of organic matter

Leaves, leftover food, droppings, dead plants: everything that settles on the bottom decomposes slowly and releases nutrients for months. A pond that has not been cleared of sludge for several years contains a reserve of fertilizer that algae exploit as soon as the temperature rises.

2. Biofilm that is too thick

Biofilm, the slimy film coating surfaces, is normal and useful when thin. When it thickens in pipes, filters, or gravel, it clogs them, slows circulation, and becomes a source of decomposing matter itself.

3. A saturated filtration system

A filter with clogged foams no longer filters: water passes through the paths of least resistance, and what has been trapped for weeks decomposes in place, inside the system. A saturated filter can return more nutrients to the water than it removes.

4. Lack of circulation

Still water warms at the surface, stratifies, and allows debris to settle in the same places. Algae take hold precisely in these zones.

5. Low-oxygen zones

At the bottom, in sludge or gravel, oxygen disappears when decomposition is too active. Yet oxygen-deprived sediment releases the phosphorus it was retaining: this is a mechanism well documented in limnology. These zones then become nutrient sources that continuously feed algae.

Address the cause, concretely

1. Observe and measure: where the algae grow, what type they are, and how long they have been present; test the water to establish reference points.
2. Remove organic matter: vacuum up sludge, remove leaves and dead plants, and take out algae by hand.
3. Restore the filtration system: rinse the foams in pond water, check the flow rate, and replace worn parts.
4. Improve circulation and oxygenation: redirect water returns and add aeration in stagnant zones.
5. Support biological degradation with suitable bacteria, especially in heavily loaded areas.

In this context, an algae treatment is not forbidden: it can help you get past a difficult stage when the pond is heavily infested. But it comes after, or at the same time as, work on the causes, never in its place.

What this perspective changes

When we stop seeing algae as the enemy and start seeing them as an indicator, we stop chasing products. We observe, correct, and the pond stabilizes. Pond owners who adopt this approach often tell us that they spend less, intervene less often, and their water stays beautiful for longer.

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Frequently asked questions

— Why do algae come back after every treatment?

Because the treatment acts on the algae present, not on the cause: organic matter, saturated filtration, insufficient circulation, or inadequate oxygenation.

— Is a little algae in a pond a serious problem?

No. A light film on the walls in clear water is normal and useful. It is their proliferation that signals an imbalance.

— What is the most common cause of algae proliferation?

The accumulation of organic matter at the bottom and in the filter, often combined with overfeeding the fish.

— Should you stop using algae treatments?

Not necessarily: they can help you get past a difficult stage, but always alongside action on the causes, never in their place.

In summary

• Algae are a symptom: they occupy an unfilled niche.
• Each type of algae points to a specific cause.
• Organic matter, biofilm, a saturated filter, circulation, and oxygen are the real issues.
• Oxygen-free sediment releases phosphorus and feeds algae.
• Treat the cause first; the algae treatment is only a support.

Last updated: September 29, 2026.