Hello,
Do to my tank size, I’d strongly caution against flat worm exit. Yes it works and has been done, however all tanks are different. If you have small rocks or not many corals, (in a 13 gallon tank), it may take you an hour to clean them. For your rocks that do not have any coral on them, just dip them in fresh rodi water. That will knock them off and keep them out of the tank. The corals I would dip in revive using new saltwater that is the same temp. Rinse them off and place back in the tank. If you have a 240 gallon tank, ahh this would be a nightmare way to do it, even a 60 would be a nightmare.
my tank is sensitive so adding flatworm exit knowing I could lose everything is too risky. Doing a six line wrasse or melanurus wrasse is much safer. With the size of tank six line would be first choice, and they would clean them up.
Even if you take items off and shake them in revive weekly it will cut the population way down, and they love nitrates, so I would run lower nutrients also. Always have carbon in your system if your going to do this. The carbon will remove the toxins from the flat worms. I was told (not sure how correct it is,) to use twice the carbon you need for the tank, to make it safe. Doing water changes that large is not ideal because it also depletes good bacteria that you need. Where your at a tuff spot is, you also have some gha, and doing water change would help reduce that as well.
I would suggest that since your treating the gha already, if you do a massive water change your throwing the medication out. So if it’s possible since your tank is 13 gallons I’d dip the rocks in fresh rodi and corals in revive. If the math is correct, it’s 1 pound per gallon, so 12-15 pounds of rock. I was able to keep mine under control just by dipping certain corals I saw them on. When I have dipped them again I get none to very few. I will say though when I dipped in rivive the first time, a lot came off and I only noticed them in a small section. I can’t see them now but when I dip corals nothing comes off which is good.