When i had jewels several years ago they started breeding at about 2-3". They were in a 29g and i remember having to remove all the other fish before they killed them.
Yea i had jewels.. They bred 3 times in m 10 gallon at my dorm... i didnt know wat to do with the babies so i threw them in with my Redbellies and even with the red bellies i came home and saw more fry months later... crazy