First, I believe that De-los is an organophosphate like Dylox or Trichlorfon. The stuff works for most external flukes, amphipods, copepods, isopods, worms etc.. , but is brutal. I have had fish immediatly turn rigid, go belly up and die within seconds from the stuff, while it has surely saved others when all else failed. Here is what the label reads - BTW - Sarin and VX gases are in the organophosphate family.
Personal Protection Equipment: All personal protection equipment on the parent label shall apply. In addition, handlers who are mixing, loading, or applying Dylox® 80 must wear a double layer of clothing, long pants, gloves, shoes, socks, safety glasses or goggles, and a respirator. Remove contaminated clothing and wash before reuse.
As for prazi-pro. I no longer use it and instead 100% pure praziquantil powder. When I would though I found out that 1.5-2x the dose for a short period would often help. Dips work great for new fish - 20mg/l for adult fish at 1.5 hr bath or 10mg/l for 3 hours for juveniles.
Prazi is not effective in all monogenia. I have had to use febendazole and even Dylox on certain flukes in the past. There are reports of febendazole causing liver toxicity in fish so I wouldn't use it first line. Stick with Prazi. PM me is you can't clear the Flukes. Formalin works too.