Mine do exactly the same thing
Even see the odd scale floating away, then getting eaten!!! :lol:
I had 6 for about 7 months, 1 died a few days ago
Not to sure why either, water properties look all fine.
Altho i have just done a big clean of the tank a few days ago.
Cool fish, but they seem to hide alot,
apart from when they are chasing each other or feeding time !!
More i think about it, i want to sell/give them away,
and get what i originally wanted in the tank ..... Guppies!!!