What is it? Is this some kind of slug?
 

I have a 29 gal with Black skirt tetra and a few of their fry (separated by divider) in it. I feed them Tetra flakes, dried shrimp and the fry get cultured infusoria and Hikari first bites. I have been doing partial water changes daily. I have been hesitant to gravel vac because of the fry, but noticed a slight ammonia spike some planaria and a population increase in the hitchhiker pond snails, so started to vac again. Before I dump the siphoned water I always take a good look to make sure no fry got sucked up. Today I did find one and kept a better eye out. Be cause of this I noticed at the bottom of the bucket there were a few tiny slug like creatures moving around. I scooped one into a small clear container. It slides around fairly quickly along the bottom and sides of the container and at first I thought it was just snail excrement. It's smaller than my fry and when it is disturbed it curls up in a u shape and floats until the water settles again. I thought maybe it was a snail baby without a shell, but I read that they are born with shells and do not leave them, so what the heck is this thing? Is it something I should be concerned about? Any help would be appreciated.

From the way you describe it maybe it's daphnia?? How about google some images of daphnia and see if that's what they are??

Its a planaria. You already said you had some too.......

pictures would help.

I didn't know they looked like that, too. I have tiny white worms on the tank glass that are very skinny which I thought was the planaria. Is it 2 different types or maybe one is a more mature form? I can't seen to get any good pictures. I'll I'll get my husband to try later.

Skinny white "worms" that move in a S-like pattern are nematodes a type of detritvor. Planaria are much larger and move "slug-like" they can shorten and lengthen their body, but can not move in a undulating S-like motion. Large planaria often have a arrow like head and visible eye spots.

The white ones are almost as thin as hair and sort of glide around on the glass. They do stretch or get really short but never move in an S pattern. Even when they are floating from being knocked off the glass they seem to just stay straight, only bending a small portion towards one end.

probably little planaria

this is an adult planaria
http://i22.photobucket.com/albums/b3...1/P1140102.jpg

This looks kind of like the thick slug like one I found today. Hopefully the little stringy guys are just the young version like you said. In that case I shouldn't worry? Just keep doing the water changes and siphons and I will eventually get rid of them?

yup. most fish will also snack on them.