Strings seem to lose power? Too slippery? Rough strings become smooth?
I have invented a device to rough the surface on the polyester and nylon strings to improve spin. It is described in details in below website. www.tennisspinmaker.com
Or in Google type in “tennis spin maker”.
I find that most strings are too slippery when they are new, and some strings with rough surface such as “Structured String” become slippery too after a short while. In both cases, the strings do not grasp the balls very well.
I am a 5.0 player and use it for all of my strings. The device is hand-made and had polished. Many players are using it too. See their feedback on the above website.