I Had the same problem a few weeks ago and now I just make up 5 gal of make up/top off water at a time and keep it in a water cooler bottle. For the weekly water changes I fill up my brute trash can with about 20 gal then add my salt,maxi jet 1200 and heater. Then use the water the next day and let the can air dry until next week.
If you keep water in the can all the time ,even with a power head moving it, it will get some kind of bacterial build up. Feel the bottom of the trash can and I'll bet that it feels slimy. Mine did. That is why I keep it aired out now and only make small batches of make up water.
Dave