There are many things you can do to avoid the nasty black ring on your toilet. The first is to use a low acid toilet bowl cleaner to kill the bacteria. The second is to get your self a really good toilet bowl brush or toilet bowl mop to scrub that acid around in the toilet and remove those ugly stains.
Toilet bowl brushes come in many styles but most are made from a material called polypropylene. Polypropylene won't mold and can stand up to heat and chemicals. Polypropylene strands are abrasive and can do a great job at removing the nasty toilet ring. The two main styles of toilet bowl cleaning utensils are the toilet bowl mops and toilet bowl brushes. A toilet bowl brush resembles a brush and has a wide stiff polypropylene bristle. Brushes tend to last a lot longer that toilet bowl mops because the bristle is larger and does not break away from the toilet bowl brush handle. Toilet bowl mops are meant to be discarded after repeated use and are considered by most to be a disposable toilet cleaning product. Toilet bowl mops have a ball of polypropylene strands massed at one end to form a light duty scouring surface. Over time the strands tend to break off and the mop should be discarded. Toilet bowl mops are usually a quarter of the price of toilet bowl brushes and most are have a plastic handle.