Cloudy pond water is usually thousands of tiny particles too small for a filter to catch on their own, which is why a filter running perfectly well can still leave a pond looking murky. Tetra's Crystal Water works on the particles rather than the filter, making them big enough to actually be removed.

It clumps suspended particles together so they either sink to the base of the pond or become large enough to be caught by an existing filter or removed with a net. Tetra describe it as safe for all fish and plants, so it's aimed at being used in a pond that's already stocked rather than only during a fishless setup phase.

• Clumps fine particles for removal
• Works with your existing filter, or via netting
• Clears murky or cloudy pond water
• Safe for fish and plants
• 250ML bottle

On the underlying cause. Tetra's card doesn't give us a dosage rate per litre of pond water or how often to reapply, so we can't tell you exactly how far one 250ML bottle goes. It treats symptoms of cloudy water rather than the underlying cause, so if the pond clouds up repeatedly it's worth looking at stocking levels or feeding as well.

Who it's for: pond keepers dealing with murky or cloudy water who want a clarifier that works alongside their existing filter rather than replacing it.