How to Remove Algae From a Water Tank

Why algae grows in water tanks

Algae needs three things: water, nutrients and light. Your tank always has water, and dust and organic matter provide nutrients. So when algae appears, light is getting in — through:

• A translucent or light-coloured tank, especially older or cheaper plastic tanks.
• A faded outer layer on an ageing plastic tank that no longer blocks sunlight.
• A cracked, loose or missing lid, or a manhole cover with gaps.
• Open inlet or overflow openings.

In Delhi NCR's long, bright summers, a tank that lets in even a little light can turn green quickly.

Signs of algae

• Green or brown patches or film on the tank walls, especially near the top.
• Green specks or a green tint in water collected in a white bucket.
• An earthy or grassy smell.
• Slimy deposits in tap aerators or RO pre-filters.

How to remove algae

From a plastic tank

1. Drain the tank and remove sediment from the floor (don't flush it through your pipes).
2. Scrub algae patches with a soft brush and clean water. Avoid wire brushes, which scratch the plastic and give algae a place to re-anchor.
3. Rinse and remove the rinse water.
4. Disinfect with a product intended for drinking water at the label dose, observe the contact time, then rinse thoroughly. See water tank cleaning chemicals.

From a concrete tank

Concrete and plaster are porous, so algae can grow into the surface. Scrub firmly, paying attention to cracks and corners, then rinse and disinfect. Badly worn plaster may need repair to stop algae returning.

Don't use household bleach in large, undiluted amounts, or "algae killers" sold for swimming pools or ponds — they're not intended for drinking water.

How to stop algae coming back

When to call professionals

If algae covers large areas, the tank is large or hard to reach, or it keeps coming back, a professional cleaning with proper de-sludging and disinfection is worth it. Our team will also tell you if your tank is letting in light. See overhead tank cleaning — from ₹499.

Algae removal from water tanks — what works

Algae removal from water tanks needs two steps: physically scrubbing the green layer off the walls, then disinfecting. Chlorine alone bleaches algae but leaves it stuck to the walls, where it regrows. After cleaning, stop light getting in or the algae will be back within weeks.