Black mold line in toilet!!

Try cleaning the tank as well....pour baking soda followed by baking soda inside

Have you tried using a magic eraser? It worked liked magic in my toilet. I used it three weeks ago under the lip of the toilet and it hasn't come back since.

I poured bleach in my tanks then after it was flushed out I keep a cake made for toilet tanks in them.

Don't use bleach in the tank. It breaks down the plastic and rubber components over time. Pour about one cup of vinegar in the tank. Vinegar kills mold better than bleach. Then pour some vinegar and baking soda in the toilet.

Try adding bleach to the tank, it may be contaminating the toilet bowl.

I heard denture cleaner tablets will do the job, buy generic ones at dollar store and throw in your tank and toilet