I did too, and it was the only thing that wiped them out from my tanks, but this only works if you don't have fish that will eat all the nudibranchs. I did clear it out of four of my tanks, though.
Aiptasia-X is semi-effective some of the time; new polyps are guaranteed.
F-Aiptasia is great at cementing them in, but won't get rid of those in your plumbing.
Hot water is free and will help to control -- but not eliminate -- them.
Nudibranchs are incredibly expensive in Canada -- 5 for $100 is the best rate you can get, but I've seen them go for upwards of $40 a piece -- but will get rid of them completely. But not if something else eats them first.