| If you used PP per the instructions on the koivet board, about the only parasite you might have left is flukes. Typically with flukes you would see the fish "flashing"... scratching against the side of the pond to get rid of the buggers. Unless flukes are visible under the scope, I'd not treat with anything more for parasites at this point. These medications are all stressful to the fish. Give them a day or two to perk up.
In regard to antibiotic medicated foods, you will get a variety of views. Undoubtedly injections of an appropriate antibiotic is preferable, but these can strain the liver and other internal functions. Antibiotics should only be used if a bacterial infection is present. If there is a visible wound, ulcer or "fin rot", antibiotics are indicated. Internal bacterial infection will often be accompanied by a pinkish, inflamed coloration in the abdominal area, particularly around the vent. If none of these symptoms are present, I would not use an antibiotic. For most fishkeepers, injecting a fish is too advanced to contemplate; and it takes a degree of skill to avoid injury to the fish. Medicated food is certainly easier to administer. Folks will tell you, however, that if an infection is serious, the koi won't eat any way. If they do eat the food, there is no control on dosage. All reasons why medicated foods are not the best choice. But, when an infection is present and you get at it before it becomes so serious as to eliminate appetite, medicated food is certainly better than no treatment at all. I have used medicated food in the past when there was a spawning injury. I believe it helped heal the wound before a serious infection set in.
I don't know if any of this rambling helps you with your situation. It is tough to give specific advice without seeing the fish in person and observing their behavior... and checking out the water conditions, etc. These sorts of problems almost always have their root in a water quality issue. |