Was planning to do a water change this morning and noticed some crud on the bottom and sides of my Brute mixing/storage container. It also had a somewhat funky smell when I removed the lid. I've noticed the smell before but the growth, or whatever it is, is something new. The mixed saltwater has been in the container for a few weeks. I keep it covered, I don't heat it, and I don't have a powerhead running in it. Photos are attached. Is this a concern? I don't want to introduce something into my DT that will cause problems.