Re:Tiny unknown creatures

     >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? 
     This sounds like a harpacticoid copepod, which is a small crustacean.  
     Most copepods are planktonic, but some harpactacoids are benthic.  It 
     is probably grazing on the algae growing on your glass, and you can 
     bet they're on your plant leaves and gravel as well.
     The two tails are called caudal rami (try to use THAT in normal 
     There is nothing to be concerned about.  They will help keep your 
     algae down, and would be relished by fish fry.