Tension level
Moderate tension (18 kg to 23 kg) will give you more comfort, spin and power. However, the trade-off is less control and precision.
High tension (>23 kg) will give you more precision and control, but you'll need to be wary of tendinitis. You'll also give up spin and power.
Monofilament strings
Decathlon recommends a tension of 19 kg to 22 kg for monofilament strings. We strongly discourage using monofilament strings for children under age 15 to prevent injury. These strings are best for players who break their strings in under 10 hours of play because they quickly lose their tension.
When to change your strings
Your racket's performance depends equally on the frame and strings! Be sure to choose the right strings.
For frequent string breakers: change your strings when you break them.
For those who never or rarely break their strings, Decathlon recommends changing your strings based on how frequently you play. For example: If you play once a week, change your strings once a year. If you play three times a week, change your strings three times a year.
Tips from Decathlon
You should never tighten a loose string pattern - it will have an outsize effect on performance. Looser strings let players play a more relaxed game without forcing to give them more power. As you play, the strings will wear out, even if they don't break. They lose their elasticity and initial properties. The gauge (diameter) also affects the feel. The smaller the gauge, the more power and spin you'll have. The larger the gauge, the more robust (and harder on your arm) the strings will be.