If you haven t cleaned the debris out of your gutter yet do this first with a garden trowel.
How to remove stains from white gutters.
Apply product allow to penetrate for 2 minutes and wipe or rinse clean.
Dip your scrub brush in this solution and scrub off the stains.
It is actually pretty easy with the right material.
Removes tough outside stains like mold mildew oxidation tree sap and bird droppings.
Scrub the gutters with the soap mixture to clean them.
On stubborn streaks let the chemical dwell longer being careful not to let it dry.
Apply the chemical according to the manufacturer s instructions.
If it is mold it will come of very easily with bleach.
I clean this for customers all the time and the product to use is called gutter zap.
I assume from what you have described it is a white gutter with aluminum oxidation on it.
You may also try mixing one quart of water with 1 cup of bleach and 1 teaspoon of dish soap.
Simple ready to use formula.
You just spray it on let sit for a few moments and then wipe it off with a damp clean cloth or rinse with clean water.
Using a power washer clean your gutters to get the initial mildew and grime off.
Climb up the ladder and spray the black streaks with gutter cleaner.
Move down the entire gutter and spray all of the spots with black streaks.
Your gutter will look as good as new.
Rust residue dirt buildup and corrosion can all be removed by scrubbing the gutters clean.
This bleach mixture will also kill any mold or mildew that s growing on your gutters.
Brush the gutter with a stiff bristle brush.
Set up a ladder at one end of the gutter and fascia where the black streaks are located.
Reposition the ladder when necessary to reach all parts of the gutter and fascia.
This is a product that will remove them with remarkable ease.
Try spraying an all purpose cleaner on the stains and scrub them off with a scrub brush.
Water based formula can also be used on mobile homes rv s and campers to remove black streaks and other stains.
Rinse with water and if necessary reapply the chemical to remaining stains and brush again.