Add a 4th or?

[secuono]

So I have 3 Angels in my 55g, they all get along, but I don't think I have a female at all. I first got the Marble & the Gold, later I got two more, but they attacked the 3rd, 4th made it a Silver. It used to be picked on, but now they all get along swimmingly. I wanted to get a Koi or another that looks nothing like the other 3, hoping it's a female or at least the trio likes it! Any chance I can add a 3rd or would it not be enough space? Any other way to tell male from female? Thanks
:feedback:

[Charlie Greiner]

If your trio are well established and getting along adding new fish may be a problem. To help reduce aggression try rearranging the tank just before introduning new fish. Then they all will need to establish territories.

[Turbosaurus]

I wouldn't add anymore.

Three is usually a bad number, one will end up picked on, but if you have three boys, you're you are very lucky. If you had a pair they woudl certainly terrorize the third.

Introducing a girl will be bad. You're going to get a lot of agression when the boys fight over her.

If you can be sure the fourth is a male, and at least as big as the other 3, you'd likely be okay, but there are no guanrantees (except that if you introduce a female you're going to have problems).

There is no such thing as "a trio" of angels. They "pair" and do not share mates without lots of fighting

[secuono]

Opps, I meant 4th*
'Any chance I can add a 3rd or would it not be enough space?'

Yea, I'm thinking I will leave it at 3.