What is this? Please

yea, probalby from the plants. You should wash the plants before you put them into the tank. I think you could use a really light bleach soltuion, but I'm not sure.
 
Dragonfly nymphs are most active at night; that’s the best time to check for them. During the day they try to remain concealed. Flip the tank light on after it’s been off for a few hours. If there’s any more you’ll usually see them dart back down toward the gravel bed.

If you’re seeing a 1cm long nymph than any other eggs would have hatched by now. Newborn nymphs are only a couple of mm long.


Tom
 
I had a damselfly larva (very similar) in my tank for a bit. They came in on some stem plants (along with a couple of killifish). The damselfly took up residence in my java moss eventually. I took him out, though, along with the leeches and isopods that had also decided to live in my java moss.

Here's more about it:
http://www.aquariacentral.com/forums/showthread.php?t=48976

It's kind of neat, really!
Tony
 
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