i answered this in your other thread, but i will answer it again mantellas are not easy to breed. they need to be cycled through seasons. this not only includes temps, but rainfall and humidity as well. and then, if you are successful enough to have a pair lay eggs that are fertile, the tads take up to a year to morph.

also, while that tank sounds big for a small species, they like to have territory, so 2 is the most i would put in there. that also decreases your odds for successful breeding. breeding mantellas is not for the beginner by any means. i wold suggest you start with d. tincs or d. leucomelas if you want to attempt breeding them.