I have a kora (West-African harp) on which the highest two strings only seem to last about a week before snapping.

The two strings are tuned to A (880Hz) and G (784Hz) respectively and are stretched 220mm and 250mm between bridge and machine head.

I'm currently using 30lb nylon fishing line, as recommended by the instrument maker.

In order to prolong the life of the strings and avoid damaging the harp, would it be sensible to replace them with thicker or thinner strings?