Koi behaviour, clay booster, upflow filter and extra air.

Over last few days koi have been behaving oddly. Pointing down, fins clamped and look asleep, occasionally flicking. Water quality is spot on, scrapes on 3 seperate fish reveal nothing apart from 3 dead flukes. Only 4 fish affected, all others seem ok. Tried Acriflavine and extra air. Upflow filter ongoing but slow due to other jobs. Added JPD mud booster to pond and clarity is great. No food given at moment, UV turned off and filter floss removed. Open to suggestions.

behaviour,booster,upflow