180 liters? I would say tank size is a big factor in this.
Both the copper band and the powder blue need a tank closer to 500 liters. 180 is nowhere near enough for them. Not to mention there i a lot of fish crammed into a small tank. Both of those are a recipe for disaster when ich is involved.
I would follow one of the treatments outlined in the link along with the fallow period. After that you can concentrate on stocking the tank with appropriate fish again.
Lastly, there are a number of ways to take care of aiptasia. Aiptasia x, lemon juice, Joe's juice, kalk
paste. Adding a fish to take care of it is not a good way to deal with most infestations in an aquarium.