Kune, you don't say where you live but the chances are the mites in your area are resistant to synthetic pyrethroids ( which what the B strips are) or if they are not resistant they probably soon will be.
If you are seing deformed wings and mites on bees then your nuc has a bad case of varroa. Use a thymol treatment as soon as possible. There are other options such as formic acid but they are more difficult to use.
Do you have a varroa floor and can you see mites on it?