Board Thread:Dragon City Gameplay Questions & Answers/@comment-9183585-20130622211458/@comment-10090661-20130719113814

All the Pure Elemental Dragons are Difficulty 2 & 3. Keep your breeding pair at either low level (under Lv 10) or high (total earning above 1000, similar levels). Other than that, Pure luck is needed. (Whee! I made a pun. xP lol)

You probably want to get another 2-3 more Pure Dragons so you can have them for both breeding and battles, though. =D