do flatworms ever go away

[Ginu]

What color are the flatworms? can you post a pic?

If they are orange and tiny they are easy to get rid of with flatworm exit. Make sure to follow the instructions and also using less is usually better and have a ton of water ready to go forwater changes along with carbon

If you have the white ones which eat acropora, you will need to dip the corals every week for 4-6 weeksand hope to kill their cyce (although they can always come back). best is to setup a QT for this task and run the tank without any acros for 6-8 months. Acro eating FW only eats acros and will die without a food source.

There is something called polyclad worms which are larger, move quite fast and they attack snails/clams