How to Keep Water Feature Water Clear: Algae, Green Water and Debris

Water goes green when sunlight plus nutrients feed algae. The fixes, in order of effectiveness: partial shade, plant cover in ponds, a UV clarifier on pumped features, regular debris removal, and topping up with rainwater rather than nutrient-rich tap water where possible. Here's the routine per feature type.

Why water turns green

Single-celled algae bloom wherever three things combine: sunlight, warmth and dissolved nutrients (from decomposing leaves, fish waste or tap water). Remove any one of the three and blooms fade — that's the entire science of clear water.

Still bowls and water tables

For unpumped water bowls and water tables, the routine is simple: skim leaves and debris weekly in autumn, refresh the water every few weeks in summer, and site with part-day shade if algae recurs. A small solar fountain adds movement that discourages both algae and mosquitoes.

Ponds

For ponds, aim for surface plant cover (lilies, floating plants) across a third to half the surface — shading the water and outcompeting algae for nutrients. Oxygenating plants below the surface do further quiet work. For pumped ponds, an inline UV clarifier kills suspended green-water algae reliably; it's the single most effective gadget for a fish pond.

The autumn rule

Most spring algae problems are made the previous autumn — leaves that sink and rot become next year's algae food. Net or skim through leaf-fall and clear any bottom debris before winter, as covered in our winter prep guide.

Frequently asked questions

Is green water harmful?

Not to fish or plants — it's an aesthetic issue, though a symptom of excess nutrients worth addressing.

Should I use algaecide chemicals?

As a last resort only — they treat the symptom, and the algae returns unless shade, plants or a UV unit fix the cause. Never use them with fish without checking suitability.

What about blanket weed (stringy algae)?

UV clarifiers don't kill blanket weed — remove it by twirling it out on a stick and address nutrients; barley straw pouches help suppress it naturally.

Does the Corten steel affect water clarity?

No — the sealed inner chamber keeps the weathering surface separate from the water, as explained in our pump and liner guide.

Clear water, warm steel

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