[Cavan Allen]

Yes, it is Alternanthera. But it's A. ficoidea, a non-aquatic.

 

[Cavan Allen]

Thank you Cavan Allen.
I'm a complete newbie at this, but I'm surprised (and a bit bothered) at how common it is for pet stores to sell terrestrial plants completely submerged in water, as if they are aquatic plants. It seems like deceptive advertising.

It's been like that for many years. Might just be because it takes the terrestrial stuff longer to die than a true aquatic that isn't happy.

 

[Cavan Allen]

Yes, you should remove it. Sometimes you see such plants grow a little but it's basically their last gasp and they don't want to be there.