The fact it's a bare bottom tank makes this an easy fix. As John said, strategically placed powerheads work wonders at eliminating dead spots. Some trial and error is often involved regarding positioning but once you've found that directional sweetspot you shouldn't need to worry about crud building up ever again.
It's also worth noting that once that crud is off the bottom of your tank making it look nice and clean, it is still in your system breaking down and adding to your bio load. Good husbandry regarding your mechanical filtration solves this problem too.
