What Is This Swimming In My Tank

[jua]

I have a 2 foot tank currently inhabited by 1 cherry shrimp and 20-30 guppy fry which are in a breeding net.

This eve I have noticed some tiny white things darting along the surface of the tank. They can be seen clearly with the naked eye, and am worried they are a parasite of some sort. What should I do ?

Also worryingly this morning I found 1 dead fry at the bottom of the net..could this be linked ?

Any ideas highly appreciated.

 

[WILDER]

Take a look here.
Check water stats.
http/www.aquarticles.com/articles/management/Ali_Planaria_Worms.html