I think you are over feeding em. Doesn't take a lot to keep em happy. When I was growing em the only feed I would give them was a little cornmeal sprinkled on top, cover with paper and wet it down. That was it for a month. In a month, turn the bed over to keep the soil loose and feed again. If you keep em cool they won't leave the bed. In 90 days you will have more worms than you can use and lots of small worms and the bed will be full of eggs.
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Ascend 133X 13' - MotorGuide Xi3 & Mercury 4