Since dart frogs should be kept with live plants....
The best substrate to use is ABG:
http://www.neherpetoculture.com/images/abgmix1lg.jpg

If you use the cocoa fiber - only- it will not drain properly.
It will get boggy---creating an unhealthy situation for the frogs and the plants

What drainage layer have you built ?
What is separating the soil from the drainage area? ( fabric? screening ?)

Springtails or springtail and isopods should be added to the soil ----> it will keep the soil/ plants healthy and provide additional food for the dart frogs

supply suggestions: http://www.frogforum.net/showthread....315#post259315