Have you considered ordering some Berghia nudibranchs online? They will always eat aiptasia, and never touch anything else. Cleaned out my 90g, and I had a severe infestation. I thought that the bergs had died (I removed quite a few and sold them, afraid that they were starving), but just last week I saw one crawling across the front glass, after four months with no visible aiptasia. They are a lasting biological control. The catch is that they aren't cheap... but you do get to sell on more than you ordered in the first place, as a general rule.
I ordered mine from
www.saltyunderground.com; they are experienced shippers and often send to Canada.