Fancy Guppies nipped fins

[Oldphoenix]

Hi! I'm new to fish hobby and I have a 20g tank with 1 dwarf gourami, 5 zebra danios, 5 fancy guppies all male, and 3 cardinal tetras. I took a closer look at my guppies recently and noticed that all of them have nipped their fins. So I observe them with the lights off at night and saw that they would chase each other and nipped each other's fins.

I'm not too sure if its bullying among them as they are also roaming and scavanging the tank as normal and eat normal as well. They also still hang around each other as if they weren't fighting at all.

I don't know what to do to stop them from nipping each other. Are they overcrowded in the tank or is it because of the lack of females?

 

[C.w.deegan]

Could be because of lack of female I always have been told keep 2 female to 1 male to prevent aggressive behavior or them from getting territorial

 

[Aiken Drum]

Is there a dominant guppy that is doing all the aggressing? If so the solution would be to remove it.

The 2:1 F/M is to stop males overly bullying females so the interest is spread out between a larger number of females. Adding 10 females would probably stop the aggression between males and pass it onto females where it can be spread out between a larger number of fish. The downside would be guppy babies and overstocking the tank.

 

[Oldphoenix]

Is there a dominant guppy that is doing all the aggressing? If so the solution would be to remove it.

The 2:1 F/M is to stop males overly bullying females so the interest is spread out between a larger number of females. Adding 10 females would probably stop the aggression between males and pass it onto females where it can be spread out between a larger number of fish. The downside would be guppy babies and overstocking the tank.

From what I notice, there is no dominant guppy. I wanted to put the perpetrator on time out so watched them carefully but all of them were doing it! They would even stay together like they were schooling but go in circles pecking on each other's tail. All of them have nipped fins, 2 of them looked worst than the rest.

I have a lot of live plants in the background of the tank, and today I added a few of my old plastic plants to give them lots of places to hide but instead they just crammed together on the right side of the tank.

I'm honestly at lost for words with their behaviour.