You want to really get rid of them. Flatworm exit works great.......BUT how you go about it is directly relevant to how many you have in the first place. If i as much as see one in my system i nuke it with flatworm exit............but when there are very few you can do that with no ill effects or precaustions taken.
If you look.........at a few of the heaviest concentrations you see.......how many flatworms do you see???
You really want to siphon as many out and then when you dose with flatworm exit, you need to have carbon ready to run in a
canister filter, as well as have anywhere from 20-100% waterchange ready....again...depending on the magnitude of your infestation. The flatworm exit is not toxic to anything but the flatworms in your tank......the toxins the worms release when they die can crash your tank if there were enough of them.......
thats why you want to physically remove as many as possible
I alos notice that my 6-line and my clown both are handy assets whenever ive used FE exit.......they both eat them as they start to float away........