Caulerpa

[Van down by the river]

Some of the free floating seaweeds work quite well.
Although you could have problems with it getting sucked into your filter intakes.
I have some, but I'm in Edmonton. I suggest check your local stores and look for sargassum. It doesn't send runners the way caulerpa species do.
You could also try some of the many other red and green macro algae species that come in on occasion. Their growth rates are much slower but they still uptake nutrients and require minimal pruning(depends on the species).
Good luck