Well it looks like Im having problems with my 2 jacks.

The smaller one which I think is a female cause it really doesnt have color and its more brownish is sitting near the surface of the water and hangs in the corner. There is no damage to the fish itself, but the bigger Jack which is darker and more bluish is picking on it time to time, just chasing it around the tank.
Any one think its just juvinish games? or maybe its just intimidated by the other size of the fish?

can you post a pic of your jacks so we can see if you have a male and female? as for the chasing it could be just an intimidation thing, a dominace thing if you have two males or breeding thing if their old enough. whenever fish start acting out of character the first thing that should be done is a water test to eliminate that as the cause.

I've been doing water changes and adding the proper chemicals, but this has been going on since I brought them home, so like you said more of a dominace thing.

I'll try to get pictures

Ok here is the Darker bigger Jack.



The lighter Jack

nice pair of jacks.

the darker one is definetly a female and i would have to say that the lighter one is also female.

at least this way you dont have to worry about them becoming overly aggressive during breeding

How can you tell they are both female?

sexing of jacks is done by the colouring on the gill plates. the females have colouring low on their faces while the males have it high on their faces. to put it another way the females look like they have beards and the males dont.
here's a pic of my male and female jack. the male is on the left the female on the right



hope this clarifies it for you