Dandruff? In fleece

Hello-I have a Black Welsh Mountain fleece that I am struggling with. It washed up nicely, and most of the VM is coming out in the picking and carding. But it still has LOTS.of dandruff or something like that!

I’ve processed and spun only a little of it to see if it would fall out, but it stays in the wool and even in the spun yarn.

any ideas for me??

Thanks!