nut advice on a paesold bass

[Tomas Bouda]

wow, thanks for the super fast response.
i have noticed this problem off and on, likely due to the extreme humidity changes in southern ontario. the point you made about changing strings is one that hadn't even crossed my mind - i have, in fact, changed my strings to obligattos, from flexocores.
i should elaborate on the bass itself:
about two years ago i began playing in fifths. so, thats' CGDA, low to high, just like a 'cello. i wonder if changing the strings resulted in altering the tension of the strings - could the nut problem be a result of this?