To kill free-floating algae( green water, in freshwater aquarium we typically use a AlgaeFix by API or the ultimate solution is a Ultraviolet sterilizer.
Here is a link to an article on our website which gives additional ways to kill or control green water: https://www.aquaticexperts.com/pages/how-to-fix-cloudy-water-in-a-freshwater-fish-tank
Here is a link to our chart - How to Diagnose and Treat a Cloudy Freshwater Aquarium Water: https://www.aquaticexperts.com/pages/cloudy-water-diagnosis
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