When should I change string?

[NikaNegin]

Hello!
I'm playing three times per week about 30 minutes. 1 h 30 min per week + one week rest in month. I changed strings 4 weeks ago from pre-strung racket(Spiraltek I played one time and I hated it to new Babolat Xcel 1.30 mm. It lost a bit power and the top cross string started a little moving. When I adjust this string, I move it easily.

Thanks for help

 

[eah123]

I think you could easily go 6 months with that string. Multifilament is fine to play with until it breaks.