Bleach--poor in dilute with water and let sit for several hours will kill mold

Have you tried a product called: Simple Green?

First I would power wash it. Than I would use the bleach and wash it again. That should get rid of it. You will have to keep it clean weekly or it will happen again

Wash it out real good and use a scrub brush then pour a solution of bleach and water in it, let it sit for a few minutes and then rinse it out really good. Try putting it in a sunny location to help prevent it getting moldy again

Bleach will kill mold.