Barrie (et al),
I used to keep a baseline sodium chloride level of about that in all my killie tanks. Velvet is a big problem with Nothobranchius spp (IMHO), especially fry, and so I always kept a eye on them and would crank the levels up if required. Species from other genera seem more robust (maybe Ps. annulatus excluded) but a low level of salt has never been a problem with the various species I've bred.
BTW: This level of salt doesn't hurt plants, not even Crypts (who are supposed to be very salt-intolerant).
There are some people who beleive that if your water quality is good enough then you don't need salt (Hi Stella) but I disagree with regard to some species of killifish.
Andrew.