Back side of plate got some of white powder

[color_prepress]

Recently after my plate come out from processor, the back side of plate got some white powder, same size of plate will have same pattern on that, different plate size will have different pattern.
Anyone know what is the problem? how to solve?
I tried to adjust the pressure of brush and roller and also clean it but not much help.

 

[aqazi81]

Clean your processor with a processor cleaner and adjust roller pressures.

 

[Steve_Reloaded]

Hardness of water and spill water into develop section may cause this problem