It looks like algae to me. Algae is easy to remove with a brush, so the
question is why does it return so quickly. I can't answer this question.

Stay away from acids and bleach. They might remove the stain but you
will have to keep applying it and it will ruin your bowl.

If it turns out to be mineral stains (usually permanganates), a cleaner
containing oxalic acid (Stainless Steel Cleaner, Bartenders Friend)
might help. Again this attacks the symptom without affecting the root
cause.

Look into some sort of filter to remove the algae. At least chat with a
plumber.


jim evans wrote:
I keep having to clean the area in front of the main jet in one of my
toilets. There's no problem with the rest of the bowl but almost
immediately after cleaning a grunge begins to grow starting at the
main jet and moving out from it almost like a liquid slowing draining
out.

Picture http://img147.imageshack.us/img147/4182/mainjetuu1.jpg

It may take a couple of weeks to grow from the jet to the discharge
area. This time I've let it go for about 3-4 weeks.

Every time I clean it I pour bleach into the bowl and let it sit for
10-15 minutes, but it doesn't prevent this.

Before the unclever cracks begin this is not crap, it's some kind of
fungus or algae, etc.

-- jim