Fritz Expel-P Gone Wrong?

[Sharkbait19]

Hello,
This question pertains to one of my freshwater tanks, but seeing that Fritz Expel-P works for both salt and fresh, I figured I could still get some good advice.

I noticed that my dwarf puffer was showing signs of an internal worm infection, so I chose to treat my aquarium with a Fritz levamisole medication. I put the proper dosage (half a packet for a 5 gallon tank) and then did the required 25% water change and redose. After the second redose is when things started to become strange, and all of my fish began to surface and gasp for air. The water also became extremely cloudy. I immediately did a 50% water change, but am holding off on running carbon because I still would like to run the medication (I probably just overdosed). A few hours later, things are looking more calm, although the breathing is still elevated. To anyone who has used Expel-P, for either freshwater and marine tanks, where might I have made an error? Should I run carbon and restart the whole process? What should I do differently?

 

[GHOSTLY]

I used to keep freshwater and still do. Put carbon in and add an airstone. Let carbon run 72h and re add medication

 

[Sharkbait19]

The poor puffer died today. Weirdly enough, it was eating and swimming just fine two days ago, and didn’t appear extremely ill either. It’s really crazy how quickly parasites can take a fish down.