Dart Den

Hello! So I have had my oaypock dart frog for about 14 months now. He has been an absolute blast and I have considered getting a second oaypock frog to add to the viv. I will attach photos of my viv. I guess my question is, is adding another frog a good idea? is my space/hiding ratio adequate enough for a second? And lastly how would I go about introducing the frogs?

My other question is since I am considering adding another frog, I would like to know if the sex of my current oaypock could be determined by somebody with a more keen eye than myself.. I will attach what photos I have. He is shy. Also I tried getting him to call by playing YouTube videos of another tinc call, but this led to my frog immediately seeking his hiding spot and not responding with a call. If that info helps any.. 
I appreciate any help I can get! Thanks to all

A second Tinctorius is fine. A THIRD would be dicey and only recommended if it was a male. Your pictured frog looks female IMO - look at the big/high hips!

While I preferred a more horizontal enclosure / hardscape for tincs and heavy bodied frogs, your design and space is good for a second frog. 

Welcome to the Forum!