Not well - city water. Could it still be algae?

Do you have soft water? If so it is a residue that accumulates when it is failing. Happend in our tank and was resolved when we replaced the soft water system.

We do have soft water, but not a soft water system - it's just what comes from the city!

You could clean that out with a bit of bleach in a bucket of water and a soft brush. Then flush a few consecutive times to rinse all down the toilet drain and away.

This is the pacific northwest and I've cleaned a lot of algae. Garden pots, patio furniture, even my deck. Then get that toilet fixed so you can keep water moving through the tank correctly and the tank covered.

Ah perfect, thanks all!!

If you clean the tank, Vinegar may ”hurt” some components . Use scrapers then bleach.

Your floor problems maybe caused by your toilet. The subfloor maybe wet and supporting mold growth.

A Mat, truthfully, my plumber hates bleach in a toilet tank. Don't ever get him started on those Clorox toilet tabs that slowly dissolve over about 3 mo. He is not a man shy with his words ;) and has said those tabs keep Home Depot doing a brisk rubber flapper business.

That's why I suggested rinsing thoroughly by filling and flushing several times.

At one time I actually liked those tabs. I never ever had to clean the bowl, only its rim and the seat, lid. If 'H', my plumber, was coming for anything I'd take the tab out of the tank before he arrived ;)

You think that soaking continuously in bleach is the same wear and tear as wiping down with bleach and water one time?

How are you doing on your sister thread re stuff on the bathroom floor? Maybe the answer is there. (Or maybe it is "a rotting guava?")

Thanks all! The floor issue and toilet are not related. I'll try brushing it off carefully and keeping the lid on as much as possible until it's replaced!

Please don't laugh; this might be worth a try. I once read an article about copper not allowing algae to grow. I have since used either a copper container or a piece of copper wire in the water of flowers. We have a small piece of copper flashing in our Brita pitcher, which we keep on the counter. It never gets algae. What if you cleaned the algae from the sides of your tank, use the bleach as others suggested, and laid a piece of copper wire on the bottom of your tank? Is it worth a try?