color of ash

so i can run my stove all day on setting 3 not problem. once i turn it up to 4, the ash like a white scale and black ash that hangs from all the horizontal surfaces.. whats causing this? any ideas?

default setting my setting
1.5" Screw Power 1 1.5"
1.8" Screw Power 2 1.8"
2.1" Screw Power 3 2.1"
2.5" Screw Power 4 2.5"
3.0" Screw Power 5 3.0"
1800 Speed Smoke P1 1750
1900 Speed Smoke P2 1850
2000 Speed Smoke P3 1950
2100 Speed Smoke P4 2050
2200 Speed Smoke P5 2150
125U Speed Fan P1 140U
145U Speed Fan P2 150U
155U Speed Fan P3 160U
165U Speed Fan P4 180U
180U Speed Fan P5 200U

still looking for ideas