Usually when any animal, including humans, come down with some kind of sickness their appetites diminish. The body wants to fight off whatever is ailing instead of making food a primary concern. I am familiar with vita-chem and I believe it to be a good product as long as you soak the food in it (something that will act like a sponge and retain the liquid). How big is your qt, how many fish are in it, and how big are they? Usually cloudy water is either from overfeeding, from a supplement (selco for example), or your biological filtration is awry. All three are possibilities at this point until questions are answered
In case you are wondering, I mention medicating for internal parasites because in the wild puffers, triggers, and other predators will scavenge for meals alive or not.