Flatworms are not that big of a deal, unless they start to smother your corals. Good flow will eliminate that problem.
Flatworms are a symptom of high light and nutrients, they will also diminish after a few months. Then, when things are looking better, you could try some Flatworm Exit--but using it now it could increase your frustrations with this hobby. I have a box of it, and have not used it yet to nuke the FWs in my clown tank--it's been 1 year since I bought it.
