This is far, far too small for dart frogs. They are specialized, and do not appreciate being mixed. A pdf would last about five minutes with a crab. You need at least 10 gallons of usable space per frog, imo (though I recommend more if you want it happy). The are poor swimmers. In a 10g paludarium, you would need to have at least 15 times the amount of usable space. Also, do you have experience culturing fruit flies?
Furthermore, leaf litter is critical for darts. I suspect that you have not done proper research on this... This is a very short list of reasons why it would not work, if you would like some more let me know. I encourage you to get into darts, but PLEASE do your research first before caring for a exotic animal.