[Nauticus]

I am a bit of a noob to the salt water scene and would like any tips on how to deal with flatworms. I have a 33G mini reef setup with a 20G refugium. The ammonia is 0, nitrate and nitrite are also 0. I have a power head and a Rena Xp4 for filtration. There is a fair amount of macro algae in the system. Halimeda and Caulerpa, the grape and cactus kind. The flatworms have mainly just shown up on one piece of live rock about a 5 pounder with a feather duster. They have covered the rock and some of the caulerpa. What can I do? I have inverts and corals so I do not want to copper them.
Thanks for the tips and help.