Diagla is base catch rate of 2%, so golden razz and nice curveballs is like 7% so nearly 20 balls needed to have very likely odds of getting it.
Are you gold in dragon or steel? That adds a 1.3x catch bonus. And if you have gotten the excellent throw down, you're looking at a 20% catch rate (2%*2.5*1.7*1.3*1.8).