Praziquantel (dewormer)

What It Treats – Flukes (Monogeneans), Black Ich (Turbellarians), and intestinal worms.

How To Treat – There are a few aquarium products which contain praziquantel: Prazipro, API General Cure and Thomas Labs Fish Tapes. Follow the dosing instructions for whatever product you are using. If using straight powder praziquantel powder, dose @ 2.5 mg/L (or 9.5 mg/gal). Powder praziquantel is not easily water soluble, but using a drop or two of Dimethyl sulfoxide (DMSO) will help to fully dissolve it in a cup before dosing.

With prazi dose once, wait about a week, do a 20-25% water change and then repeat dosage. (Or use this treatment calendar to determine when is the best time to add the second dose.) The reason for the second dose is to eradicate the “next generation” of worms before they can lay eggs of their own. Because while Prazi does kill worms, it doesn’t eliminate any eggs they might leave behind.

If you are treating a known prazi sensitive species (e.g. wrasse), you can run carbon or perform a water change 24 hours after dosing in order to limit exposure time. While praziquantel does remain active in the water column for up to 72 hours, only 24 hours are needed for it to eradicate external worms. Don’t forget to still do the second round though!

There is also a higher concentration bath dosage that you can use with straight praziquantel powder + DMSO, which may be useful for eliminating so-called prazi resistant flukes. You give the fish a 6-8 hour bath in a large glass container or food grade plastic bucket @ 7.5 mg/L (or 28 mg/gal). It is very important to both temperature control and heavily aerate the water throughout the bath. If possible, transfer the fish into a new/clean QT after the bath to avoid possible reinfection from fluke eggs in the old tank. And remember to do a second bath + transfer into a clean QT about a week later to deal with any leftover fluke eggs on the fish itself.

Prazipro is generally considered reef safe, although it may kill any tube worms/feathers dusters you have. It may also eradicate bristle worms. If you have mass quantities of these, the resulting die-off can lead to an ammonia spike. After treatment is done, activated carbon may be used to remove any residuals (if you need to use a different medication next). This is important because the Oxybispropanol (solubilizing agent) Prazipro contains will sometimes cause a bacterial bloom (cloudy water) when mixed with other meds. If using a protein skimmer post-treatment, be advised that it will “over skim” for at least a week or so.

API General Cure contains both praziquantel and metronidazole, and is an effective substitute for using Prazipro. (Just don’t follow the 48 hour repeat dosage instructions; Redose 5-7 days later instead.) But where General Cure really shines is when soaked in food to treat both intestinal worms and internal parasites (flagellates). Both maladies share one classic symptom: White stringy feces. You can also food soak Thomas Labs Fish Tapes or just straight praziquantel powder; but be aware that prazi only treats intestinal worms. (You would need to food soak metronidazole for internal flagellates.) I recommend feeding the medicated food daily for 2-3 weeks, or until symptoms are no longer present. My recipe for food soaking prazi (and metro) can be found below:

Using a shot glass:
  • 1 scoop (~ 1/8 teaspoon) of medication
  • 1-2 scoops Seachem Focus (this makes it reef safe)
  • 1 tbsp food (preferably pellets or frozen food)
  • A pinch of Epsom salt to help expel dead worms/parasites
  • A few drops of saltwater or fish vitamins
  • Stir until a medicated food slurry has been achieved
  • Feed after soaking for 30 mins
  • Refrigerate or freeze any leftovers for future use
  • You can feed this mix 1-2 times per day. Not recommend to exceed 2 feedings per day with medicated food.
  • Feed daily for 2-3 weeks, or until poop returns to a solid brown or green color (no white).

Pros – Reef safe, effective dewormer that is relatively gentle on most fish.

Cons/Side Effects – Mild appetite suppression, moderate oxygen depletion, wrasses are sensitive to overdosing. Prazi resistant worms (both external and internal) do exist, so sometimes an alternative treatment must be used instead. This includes hyposalinity or formalin (to treat external worms), and food soaking Fenbendazole to deal with prazi resistant intestinal worms.