Right now I have heavily planted 15 gallon tank, the entire bottom is covered with moss I have a coco hut, lots of african root wood, bromeliads and other small plants. There is one cobalt tinctorius in the tank and I want to add another. Is this possible / safe to do ?
adding another tinc into the enclosure can add stress to the frogs. However, tincs usually do just fine in pairs (especially male/female pairs). I've heard it recommended for at least a 20 gallon however!
I agree with Rob,
the frogs would do better given a little more space.
If you decide to use the tank you have, I would suggest removing the current inhabitant for a couple of days, and possibly changing things in the tank (moving things around, adding a plant,removing a plant) then introducing both frogs at the same time. This will give both of them equal opportunity to stake out territories.