What is the best cleaning agent to use to take green off vinyl siding

Try Wet and Forget

The green is mold. You can use a commercial mold remover for siding that attaches to your hose, or bleach water with a little kitchen detergent in it.

There is a product for just this purpose..........

Moss? Wet It and Forget It is available at most hardware/big box stores.

blast it with a power washer, works great and fast

Oxiclean or its less expensive copy found in the Dollar Tree -"Totally Awesome Orange". Put a couple of scoops in a bucket of warm water and brush away

I read that you should use powdered oxygen bleach and water, but not chlorine bleach. Wondering if the chlorine damages the vinyl.

A vinyl siding cleaner with a cup of oxygen bleach and one gallon of water mixture makes it an environmentally-friendly option. This is helpful especially if you are maintaining a landscaping wherein it will clean the vinyl without damaging anything.

I’ve used Simple Clean with a scrub brush and a sprayer on my hose. A pressure washer can do a lot of damage so I’d avoid that.