why pH 6.0 for C. elegans growth?

I am trying to find “historical” papers why C. elegans is grown at pH 6.0 using potassium phosphate buffer? So far, can’t find any.
Can they grow comparatively well at pH 7.0 or 8.0 without any effect on longevity, broodsize etc? :-\

It isn’t obvious why phosphate, since it doesn’t buffer very well at pH 6. maybe the idea was that bacteria typically acidify the medium anyhow and bring the pH down. i don’t know what the pH is in the rotting apples where C. elegans lives in the wild, but it is probably fairly acidic. but most C. elegans strains will also grow fine at pH 7 and 8. you’d have to measure longevity etc. to see if is altered for your strain. worms also are happy on Tris-buffered medium, e.g., MYOB medium.