If this is the 12"X12"X12" starter kit, I think this is just a bit small for darts, and would probably need some modifying to suit darts, as well. I'd go for something a little bigger, at least the size of a 10 gallon fish tank, i.e. 12X18X12 at minimum, to give more roomy bottom profile. These are generally rather active, diurnal frogs. You could keep something like 2 D. leucomelas in this size, as an example. The general rule is 5 gallons per frog, but 5 gallons is usually too small for one alone for any length of time, although 10 will hold two of most species adequately. You would have to modify the top screen into a hinged glass lid or some other solid top that holds moisture, or cover it with something like Saran Wrap. Otherwise, the kit itself seems pretty complete, and building your own from an aquarium tank with all included, would probably cost about the same in the long run.
In case you aren't familiar with dart care yet, here are just a few very general rules:
1. Temperatures between 65 at night and up to 80 during the day.
2. Humidity between 80 and 100%. They are rain forest species.
3. Small tropical plants in some sort of organic substrate, either a "jungle mix" compost, coconut fiber, sphagnum, leaf litter, or a combination, without added fertilizers, pesticides, vermiculite or Perlite.
4. Light in the 6500 range is for the plants. No UV, since the frogs don't bask and their food (usually fruit flies) is dusted with vitamins and calcium with D3, so they don't require it.
5. A drainage layer or a false bottom to either collect and sump-off, or recirculate water, depending upon the design.
6. Misting. This is done either by hand with one of the many choices from simple water spray bottles to more fancy misters. Some set-ups with false bottoms and pumps circulating the water over falls or drip walls, seldom require misting.
7. A living background of some sort with epiphytic bromeliads, such as Neoregelia, mosses, and climbing vines is utilized by all of the darts that I have experience with, even those that are more terrestrial than others, and it gives them more territory. It is essential for most of the thumbnails. The backgrounds can be built from cork bark, pressed coconut panels, even Great Stuff covered with coco fiber and moss.
There are as many ways of building a dart tank as there are people who do it, and most of these ways work for them. I think LLLreptiles also has Exo-Terra set-ups, and although I've never tried them, I've seen them set up for darts at a frog show, and they look pretty good, albeit still somewhat small, in my view. Other people have found them satisfactory. I'm of the "bigger the better school," however, so you should get some other opinions.
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Patty
Pahsimeroi, Idaho
D. auratus blue
D. galactonotus pumpkin orange splash back
D. imitator
D. leucomelas
D. pumilio Bastimentos
D. fantasticus
P. terribilis mint and organe
D. reticulatus
D. castaneoticus
D. azureus
P vittatus
P. lugubris