When you get a chance to photograph the other one as well, take a couple of close-ups of the front toe pads of each so we can all take a guess about the sexes.

That's a nice vivarium, by the way. It's always tempting to plant too much at first, then it all over-grows too quickly. This should afford them some nice hides with a lot of open space for feeding and viewing.
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Patty
Pahsimeroi, Idaho

Dendrobates: auratus blue, auratus Ancon Hill, tinctorius azureus, leucomelas. Phyllobates: vittatus, terribilis, lugubris. Epipedobates: anthonyi tricolor pasaje. Ranitomeya fantastica, imitator, reticulata. Adelphobates castaneoticus, galactonotus. Oophagia pumilio Bastimentos. (updated systematic nomenclature)