White film when mixing salt water

[Phanman]

Ive been planning to add 2x 20gal tanks to my existing setup and so far 1 has been hooked up and everything is fine. Now ive been mixing the salt water in the 2nd tank for a week before the plumbing goes "online" and I have a white film on all sides of the glass. This didnt happen to the first tank so not sure if I should either

1. dump the water, clean it out and start again
2. clean the dust off with my hand and try to siphon up the white film
3. just let the filter sock do the work

What do you guys think...