If pond water keeps turning green no matter how often it’s cleaned, a UV sterilizer is usually the fix, not another filter.
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What It Actually Fixes
UV sterilizers kill free-floating algae cells and some pathogens as water passes through, which clears ‘green water’ caused by suspended algae. They don’t affect algae growing on surfaces (string algae), which is a different problem.
Sizing Note
A UV unit needs to be matched to both pond volume and flow rate; too fast a flow rate reduces exposure time and cuts effectiveness.
