I've always made up fresh saltwater in my Brute and let it mix for 24 hours via a powerhead and used it. I recently mixed up a batch (18 gal) and had it circulating in the same Brute can for 6-7 days. I turned the powerhead off and noticed a short time later a film on the water surface. I guess it was some type of bacteria bloom that was happening in the water and the powerhead kept it stirred up enough that I did not notice it. I would think with RO/DI water (TDS at 1)and new salt (IO) that it would take longer for this bloom to get going. Has anyone else noticed something similar when allowing fresh saltwater to mix for about a week or so before using?

Brad