Revenge of the black algae

This is the worst thing that can happen to your washing machine. Yes, our LG top-loader got invested by black algae. We did not notice this as it was hidden between the inner steel drum and the outer plastic drum. We tried everything: several repetitions of the tub-clean program (wash, rinse, repeat), a full hot water load, even tried a swimming pool algaecide.

The greater part of the solution was to remove the upper ring that shielded the space between the inner and outer drum, and using a thin bottle-brush to brush the algae off. After that we let it stand for several hours with a swimming pool shock-treatment product to remove the last traces.

Moral of the story: do more full loads, and leave the machine's lid open to dry out properly. Perhaps even leave a day open to reduce the time the drum is wet.