I've had very good success with FWE, its completely harmless to your tank inhabitants. If you see FW in your DT you can be sure they are in the whole system, including the sump/refugium. IMO the Wrasse will likely not be able to keep up with them, and will only, at best, keep them at bay in the display only, yet they will continue to thrive in the sump.
Like Zooid stated just have lots of carbon ready, siphon out as many as you can before hand, and have enough water ready for a big water change after.
Dose 3-4 X the recommended dosage, and for good measure repeat a week later.
The FWE itself is 100% safe and will NOT harm anything, it is the toxins that will be the issue. Follow the directions with the exception of dosage, and you will be good to go.
I personally would not wait I would do it as soon as you can. They produce exponentially. Just do it you won't be sorry.
Good luck
HTH