[clifford]

I don't think I've seen this in my tanks before. It reminds me of hornwart, but is much more plastic like, less branchy, and more uniform with rings every inch or so down the stem.

Sorry for the lousy pic, the plant in question is running across the lower half.

Thanks!

 

[clifford]

My camera is not stellar, and my photography is worse, but here are two attempts...

I would not be at all surprised if this is an invasive weed (that probably came with some koi via the local fish club), but I don't think it looks like the photos of the two species you guys mentioned. Similar in structure to the muskgrass, but thicker. It literally feels exactly like a plastic aquarium plant, but is not.