If mold or mildew is the culprit spraying with a bleach solution will remove it.
													
																	How to remove algae from aluminum siding. 
									
	
		
	
																	It s not uncommon to have a mildew problem on aluminum siding depending on where you live. 
																	Mildew and algae on vinyl and wood use a solution made of oxygen bleach not chlorine bleach mixed with water. 
																	For those tough spots use a gentle. 
																	Spray this mixture on remaining spots. 
															
													
									
	
		
	
																	Stains on wood cleanse with mild detergent mixed with water. 
																	Choose a cleaning solution that is appropriate for the type of growth you have on your siding. 
																	To 1 quart and use it in the same power washer as step 1. 
																	To clean aluminum siding having mildew use a solution of one part bleach and four parts water. 
															
													
									
	
		
	
																	Water stains remove with a mild detergent and water.