Hello , friends ,I have a pond with approx 1000 gallons and 10 fish,including one very large koi ,however over the last few weeks I have suffered from low oxygen in pond ,this has been put right my adding 4 extra airstones and cooling of temp was 26 now around 17- the low oxygen affected my big koi ( see prev post ) but Im pleased to say he seems fine now .However over the last few days I have noticed 3 fish flashing ie seemingly trying to scrape parasites off them ...but on looking at fish they show no signs s of any thing untoward in appearance ..Also recently I have noticed my water looking slightly green so I have today replaced thr UV bulb with a new one .Now my dilemma is this ....if I do indeed have parasites then treating for it (NT labs anti parasite) would involve switching UV off for at least a week and ive only today put a new bulb in to get rid of green water AND it would also reduce oxygen level again .....SO it seems im caught in a catch 22 situation ...I am concerned at 3 fish flashing ( including big koi ) but not sure if adding anti parasite is the right thing to do due to reasons just given ,would a partial water change help?? Can anyone advise me what my next action should be ? Also I have tested all paramiters and all ok ...weather in Surrey warm and humid .