Algae and blooms in a pond - how to deal with them
Green water, algae coating the banks and plants, a “scum” on the surface - this is a common problem of ponds, especially in summer. Usually it is not a coincidence but the result of an excess of nutrients and light. The good news: it can be reduced if you tackle the cause, not just the symptom.
What drives algae
- nutrients (nitrogen, and especially phosphorus) - from fertilisation, run-off, feed remains, leaves, animal droppings,
- plenty of sun and warm water,
- shallowness and poor mixing - they favour warming and stagnation.
It is the same mechanism as eutrophication, only on a small scale.
What really helps
- Limit the inflow of nutrients - this is the basis: less fertilisation in the surroundings, clearing away leaves and remains, sensible fish feeding.
- Competing plants - aquatic vegetation (submerged, floating) takes nutrients and light away from the algae.
- Shade - bankside plants or shading part of the surface limit excess sun.
- Aeration and mixing - they improve oxygenation and hinder stagnation.
- Mechanical removal of filamentous algae and the “scum”.
What to avoid
- Drastic “anti-algae” chemicals without diagnosis - they can kill off the oxygen as the biomass decomposes and make the situation worse (a risk of a fish kill).
- Acting only on the symptom - without limiting the inflow of nutrients the problem will return.
Caution: cyanobacteria
If the “algae” are a cyanobacterial bloom (scum, streaks, smell) - be careful (toxins) and proceed as in the article Cyanobacterial bloom - what to do.
In practice
It is easiest to act ahead of time, by observing transparency, oxygen and nutrients through the season. In LimnoLog you can keep these indicators in one place and notice when the water starts to “turn green”, before the problem grows.
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