Big bro, how are you? Seems you have green water problem...?
UV use for short-term measure until the grapes grow out lah, else consider shading the pond first? Green water problem confirm due to high light exposure. The clearing up you experience usually due to the algae absorbing the nutrients in the water, but once clean, the algae build-up again and it's all back to square one leh.
So effectively, you either target the nutrient problem or algae problem and it should solve the green water issue.
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