Thank you for all your answers and shared ideas, friends!
Is a long story how I started with guppies, but after only 7 babies survived among the about 12 adults I bought for first time, I happened to have about 100; al descendants of the 7 survivors.
I always intended to have the Fancy type with strong colors (blue, turquoise, red, etc)
I never picked at the store any of that type (Cobra).
Anyhow, those Cobra where born about 2 months ago, and recently I added 3 new males (blue, orange, orange/turquoise)
and it happened that the Cobra started attacking them on end!
The don't attack the previous deep-color-long-tail males. Just the new ones. I ended putting them separately!
Thank you for all your help, again!