Algae eater?

I really think shrimp would be your best bet for that, although I can't tell if the stuff in the photo is typical thread algae or clado. If it's clado, you won't find anything that will touch it.

Is each little filament tough like a spiderweb or is it soft and slimy?

I wonder if a farlowella would do the trick. They have a good reputation when it comes to hair algae and they'd probalby be good tank-mates with your alutms. I've never kept them personally but it's about the only thing left. Otos, corries, and plecos won't eat that stuff.