Dipped all my euphyllia. 11 pieces and this was the outcome. My questions are…
1. Will consistent dipping treatment eradicate completely or will I always have to be on the lookout for flat worms?
2. How many days apart should I dip?
3. How long should I continue the dip process to ensure I catch all hatched eggs?
I believe I've seen these referred to as polyclad flatworms or euphyllia eating flatworms. Dipping all your euphyllia is a good move.
1. Yes, but they do lay eggs so if you can scrape those off as well that will help (see link below for pics).
2. I am not sure since I have not personally dealt with these. I would search the forum for the above flatworm names and see what others have done.
3. At least a few weeks if not longer. I saw a thread where someone did it for 8 weeks I think and they didn't come back after that.
Here's a semi-recent thread with pictures of eggs for reference:
https://www.reef2reef.com/threads/beating-euphyllia-eating-flatworms.967166/
Hopefully someone who's more of an expert can chime in, but in the mean time this should help get you moving in the right direction.
Best of luck!