Now I'm getting better at darkroom, I'm getting more particular. I sometimes (not always) get minute black specks on negs (not hairs, and am 90% certain not airborne dust). These specks are very very small and roundish - i.e. not threadlike in any way). My feeling is that it's c**p in the mains water. I have a filter I haven't fitted yet, but my question is:- is there anything else that can cause this? What have others found is the no1 cause of specks on negs apart from airborne dust?