I think it is called Baby's Tears (Soleirolia), I have a spot in my garden that it grows well in, so I just pull some up every now and then.
This evening I ambled down to the shed and had a lovely surprise![]()
I thought I had lost one of the group and despite giving their tub, what I thought was a thorough search I found no sign of it.... I checked it at least twice, removing all the leaves and hides. This evening I found all three in the water![]()