Holes in walls and flat surfaces

Hi All,

I am a few weeks into using a new Monoprice Maker Ultimate 3D , I have had one successful print. All other prints have had problems where the flat surfaces do not fill in completely. They end up with voids and holes when printing something that is supposed to be flat or filled in. I am using a black Monoprice PLA filament and am wondering if it is a problem with the filament? I have repeatedly calibrated the bed, replaced the nozzle and cleaned out the hot end.

Any advice would be greatly appreciated.

Thank you