Old equipment maintenance - thin flakey layer of crud

[WuHT]

My issue is that I like to keep some available salt water ready for an emergency water change for about half a year now. I have purchased a larger brute rubbermaid container (roughly 30 gallon), and keep it in a mixture of water, IO salt, ph buffer with a powerhead and a header running.

The issue is that , the bottom of the brute container AND the surfaces of the powerheads and heaters look to grow a thin semi opaque beige layer that flakes off if I scratch it (or sometimes it's too hard to remove). I have no idea what it is, but I notice it's only if i keep my saltwater in a rubbermaid container. Is it a mixture of the plastic reacting with the salt water ?

How should i handle this (or is it even normal) ? Vinegar bath all my equipment ?

Thanks for the advice