Photoshop cc 2017 layer mask erasing

GOLDENORFE

im having a problem using the brush tool when erasing parts of masks , set at 100% opacity and flow i cannot fully erase the part of the mask i want , getting ghosting of the layer being erased. looks like about 10 % opacity left any ideas ?

GOLDENORFE

this shows what i mean , a fully erased duplicate layer still shows through!