@svalli I had the same problem when I started seeds in granular DE. I now will mix DE with another starting mix or worm castings with far fewer helmet heads than if I used the straight DE.

I gave the replacement seeds an extra dime thickness of dirt and a couple of cool nights off the mat, they came up this morning clean cots with nary a seed in sight. Extra dirt gets some credit for the fact they even left em buried. Alternating heat and cool makes sense too from a condensation perspective I think. Those seeds softened up better.