I experienced something strange in the last couple days with my baby guppies. (Born Jan 19): Their tailfins started to go from a nice wide fin to a really thin fin. the end of the fin comes together in a tip
like that: ===>
In addition, their spine seems not straight horizontal anymore. It lookes like the spine is turning into a 'u'
My other fish are healty, only my baby guppies (still in breeding net in main tank) have that.

What the heck is going on???

Elli