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