I think this may be similar to Nayfee's post about thread -like worms....
I was examining the cycle tank and took a close look at the mossball (which was in a live tank in the LFS) and it has loads of life in it. Some little specs that jump over the surface and a worm that peeped out and went back in. All smaller than grains of sand, and can't make out anything other than white blobs...
I'm happy I have some creatures! Any clues do I need to take any action?
They sound like the normal critters you get when cycling a tank. The worms could either be planaria (flat worms) or detritus worms (look like little hairs) and the jumpy things are probably cyclops (a type of copepod). They are harmless enough, not sure if your shrimp will eat them when you introduce them but they will probably die off anyway once the shrimp start eating all the food.
Sorry to resurrect old thread, but I've done a bit more research which may help some people out.
Planaria are harmless to fish, but do cause harm to shrimp, and can kill healthy adults. Advice to remove them is cut down on feeding and gravel vacuum plenty. Alternatley set up a trap to lure them out and fish them out.
Luckily for me I don't have planaria, but enchytraeus worms in my tank, which i think are harmless, but there doesn't seem to be much info on them. ...
for ID purposes - planaria = white, short and flat worms, enchythraeus = white, long, thin and 'wiggly' worms (can't think of a better description lol ).
Looks like detritus worms to me. They're very common and since you've just cycled with fish-food there's probably been a bit of a population explosion. They can come in initially on gravel, plants or whatever and you don't normally see that many unless overfeeding the fish - or in this case feeding an empty tank !
They're harmless and numbers will decrease with some gravel vac'ing and the addition of livestock.