Bill Cody taught me that some shiner species need much tighter gaps, almost better described as crevices. They need gaps more like 1/4" or so.
Fatheads don't need the crevices, just the spotfin shiners. Maybe bluntnose minnows too. But if the crevices are desired, and you still need weight to keep down the pallets, what about using cheap gravel to weigh them down? Then you would also accomplish the crevice spawning habitat as well.
