Look lik E. tenellus Japanese hairgrass look similar to Eleocharis parvula, the different is the leaf curl down instead of straight up. Eleocharis sp mini at Tropica web side is look exactly like Japanese hair grass. http://www.tropica.com/en/plants/plantdescription.aspx?pid=132B
And a name check on it for Tom, not bad that. Yeah, E tennelus most likely, I just thought blyxa because of how it's melted at the tips, I found the E T melted near the root rather than the tip.
I have to say I am doubting the E. tenellus...i think it something else...not blyxxa or any Eleocharis. I'm leaning towards Acorus gramineus, a bog grass like sweet flag sometimes sold as an aquatic. The browning of the tip, Garuf pointed out doesn't appear to be the type of melting you would see in an aquatic. C. helferi can brown at the tip when cut, but it doesn't usually extend far below the cut or break. Another option would be dwarf mondo grass.
I honestly think it's blyxa still but I'm happy to be proved wrong, I'd chance it and keep co2 high and see how it goes, unless you think it's not gonna come back in which case i'd switch it out for Acicularis.
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