Maybe the clouding up is a bacterial bloom, which with all the water changes, could be taking longer to finish. I think 50% daily is a little much, I know your trying to heal the FH but maybe drop it 50% ever 2/3 days. Also try putting some clean filter floss in the filter.
You know just cause a fish looks peaceful and harmless during daylight hours, doesnt mean they dont turn when the lights go out.
Its either the pike, GT or Sushi. Anyway sorry for your loss.