Re: Tiny unknown creatures

Hi Learned List Members

The other day, just after lights on, I noticed these very small
organisms flitting along the glass. They were/are *really*
small (about 1mm or less). I only noticed them against the dark
background. They were oval shaped with two tails at one
end. They moved around with quick darting bursts. The fish
(discus, clown loaches) paid no attention to them.
Does anyone know what these are? Should I be concerned? 

Thanks in advance

Marshall Wilkinson
Calgary Alberta