Residue on RO/DI

[Jimmyneptune]

I have some ro/di water that I stored in my salt water mixing vat, approximately 15 gallons, which is loosely covered. It has been in the container for 3 weeks. I opened the container and it seems to have an oily or dirty residue on top of the water. Storage area in a closet off of laundry room/ furnace room.

Any ideas what it could be? Can it still be used safely?

 

[landlubber]

i don't know about a "slick" on the water surface but i've certainly wiped my rodi storage vessel out plenty of times and removed modest amounts of brown gunk. i just make a point of doing it whenever its empty and i remember.