>- think that 2,5 K is a good compromise?

Actually, no. In my book, I recommend using both 2.5 kHz and 30 kHz for best results. It does take longer, but according to customer survey response, using both does produce better results.

7-7-20-7-7-20-7-7

7 minutes at 30 kHz, 7 minutes at 2.5 kHz, 20 minutes off.

Longer than 7 minutes improves results i.e. 10-10-20

Repeating more than 3 times improves results.

However, do not start out this way. Start with regular zapping and increase after die-off has reduced.

The book parasite Zapping and the Zapper provides this information and much more.