I have a 55 gallon food safe storage drum that I keep my mixed saltwater in for water changes. The water comes from my RO
filter and I use Instant Ocean Reef Crystal salt mix. I have a circulation pump and a heater in there that keeps the water at 80 degrees.
After a few weeks, I notice a pasty cream color residue that covers the pump and the walls of the drum. Is it mildew? Is it something I should be worried about? My coral and fish don't seem to be affected by my water changes.
The drum can be sealed air tight, however I have one of the bung holes open to feed the power cords into it.
I've attached a photo if it helps. Thanks for your help!