|Pacific rose seaweed, Rhodymenia pacifica|
This seaweed, common enough among the scraps tossed up on the shore by the tides, but usually out-competed in the intertidal zone by the sea lettuces and rockweed, is the only one that loves its home in my tank. Other seaweeds float around, sometimes for a couple of weeks, until the hermits and crabs have worn them to shreds. Eelgrass holds out a bit longer, but eventually turns black and disintegrates, leaving only the roots.
Rose seaweed grows and grows and grows. I rip out handfuls every time I clean the tank. But it's a popular hangout; the handfuls always come with a crowd of amphipods, a couple of hermit crabs, and maybe a snail or two. I have to wash them out carefully and return them to the tank.
So I always leave a small clump, usually attached to a rock. And a few days later, it's grown and taken over half the tank. I think it likes it here.