I found my pre-mixed saltwater in the brute can developed some sort of bacterial slime and really smelled bad after a week or so. It was because I wasn't circulating it. After cleaning the brute can thoroughly, I mixed salt water again, kept the MJ running in it, and it kept fine. I only put the heater in the night before a water change. I know I'm only saving pennies in electricity that way, but every penny counts.