Nothing spoils a garden pond faster than pea-soup green water. You’ve stocked lovely fish, planted the margins, and yet all you can see is a murky green haze. It’s one of the most common questions we hear from pond keepers across Northern Ireland — and thankfully, there’s a permanent solution.

What Causes Green Pond Water?

Green water is caused by billions of microscopic single-celled algae suspended in the water. Unlike blanketweed, you can’t net it out or treat it by hand. In Northern Ireland’s bright summers, these algae multiply rapidly, feeding on nutrients from fish waste and run-off.

The Permanent Fix: UV Clarification

A UVC pressure filter passes pond water over an ultraviolet lamp, which causes the algae cells to clump together. The filter foam then traps those clumps, leaving your water crystal clear — usually within one to two weeks of installation.

Our top pick for most garden ponds is the Bermuda 10,000 18W UVC Pressure Filter. It combines mechanical filtration, biological filtration and an 18-watt UV clarifier in one sealed unit, suitable for ponds up to 10,000 litres (or around 5,000 litres if heavily stocked with fish).

Why Pressure Filters Suit NI Gardens

• The sealed design can be partially buried, keeping it hidden from view
• Water can be pumped uphill to a waterfall or stream return
• Simple backwash cleaning — no need to open the unit every week
• Handles Northern Ireland’s leaf fall and heavy rain run-off with ease

Your Local Pond Filter Specialists

Clearly Aquatics supplies pond filters, UV clarifiers and spares across Northern Ireland. If you’re not sure which size filter your pond needs, get in touch and we’ll help you calculate your pond volume and match the right unit. With the right filtration in place, green water becomes a thing of the past — all summer long.