I used to have a lot of guppies at one time always males though as i didn't want the breeding and i got some danio's, never again aggressive or what and towards my guppies and my guppies used to keep out the way so i soon removed them and they was took to our local store.
I've never touched them since.
The tank is 6 months old I used the fish in method and the tank had to be fully cleaned and recycled after a goldfish that was purchased had a parasite and wanted to make sure I got rid of it before getting new fish then NITROGEN cycle spike happened 2 x and I waited to clean to build up the bacterias in the tank to make sure it fully cycled. It worked. I used test strips as well as the liquid to test water. All levels are at 0 ppmPlease keep in mind that all advice given here is free of charge, and it is up to the OP to take or leave that advice.
We are here to help, not to disrespect. The advice given is in the best interest for the well-being of our fish, and the peace of mind for the fishkeeper.
The most important factor to consider for the health of our fish is the water parameters (conditions) our fish are living with in our tanks...specifically, ammonia, nitrIte, and nitrAte levels in the water. First and foremost, we need to know these levels before considering other factors that may be contributing to detrimental behavior or health of our fish.
Again: How long has the tank been set up?
What kind of cycle did you perform, fishless or fish-in?
What kind of test kit do you use?
What are your readings for ammonia, nitrIte, and nitrAte?