Because they start breeding at 4 inches.
The OP is asking if they will - and the answer is yes.
Like I said, should he? That's a completely different question.
And, to answer the question more specifically; in my own opinion, a 75 is plenty for a pair. I've had a 55 gallon with 3 or 4 pairs breeding simultaneously in the past - it was quite a colorful, active tank.
If the male (or female, for that matter) is overly aggressive, then a divider could work.
The best way to get a happy, compatible pair, is to let them pair off naturally.
yeah i know they will breed in a 75 i am asking if it is a good idea to try to breed them in a 75 because it is the only open tank that i have atm. i think i am going to try it and see how it works out.
thanks everyone!