Sad Red Wag Platy

the ph is 7.4
everything else the pet store said was good.
temp is 76-78

I have a 40 gallon breeder tanks with 1 red ear slider turtle and 2 Mississippi map turtles (all babies)

2 platy one baby platy (gave the rest away) one looks really sad the other one is hiding alot the baby is always out. the one always did hid nothing new the other was out and very happy.
2 mollies with several babies (gave some away)
4 guppies One looks sad too tail drooping down 3 Babies. (gave most away)
ghost shrimp (several like 15)
3 mystery snails
All are eating well
they are rubbing on everything.
http/s801.photobucket.com/albums/yy292/sallyjayd/?action=view&current=P1060048.jpg
http/s801.photobucket.com/albums/yy292/sallyjayd/?action=view&current=P1060047.jpg
http/s801.photobucket.com/albums/yy292/sallyjayd/Turtle%20tanks/?action=view&current=P1060032.jpg#!oZZ2QQcurrentZZhttp%3A%2F%2Fs801.photobucket.com%2Falbums%2Fyy292%2Fsallyjayd%2FTurtle%2520tanks%2F%3Faction%3Dview%26current%3DP1060031.jpg
videos
http/www.youtube.com/watch?v=JWptqyX8-x8
bad but you can she her so sad?
What should I do? Is this from her being sick?
or maybe stress
the guppy I can see a lump on her spine right in front of the tail you can see her in the video but not the lump looks to be inside

everyone else seems very happy.
except for the 2 plays and the 1 guppy
there are lots of places for them to go the turtles can't get to. the turtles leave them alone for the most parts.

Please help I want everyone to be healthy, and happy.
http/www.youtube.com/watch?v=OBHwAswizpA