I been following your plight, you mention its new (tank).....how new and how much livestock is in the tank?
To find a suitable treatment, you should first start by becoming an expert to your enemy and see what its biological vulnerabilities are and what if any current modes of natural control are. Then you can begin to make educated guesses if levamasole or perhaps Interceptor (some methods for controlling SPS pests) would work on that species effectively.
For instance, while researching AEFW's I found that Levamisole works in a certain way just like your ivermectin.
http://en.wikipedia.org/wiki/Levamisole
http://en.wikipedia.org/wiki/Milbemycin_oxime
Anyway, I had fun with that research and I am sure you will learn a ton yourself so you can pass it along to the rest of us.
(You can find Levamisole at Tractor Supply, but research its reef aquarium applications before using)