Dale, "the guy at the expo" (someone trying to sell an animal, I'm guessing) gave you information that contradicts every care sheet I found in a quick web search. (That size viv is marginal for a crested gecko, too.)
I don't know what the 'bioactive' people are doing these days (I keep darts, but dart keepers try to stay off bandwagons), but recycling drainage water in a viv isn't a great idea (the drainage water is wastewater). If I were you, I'd consider rethinking the design of your viv. Since you can't rule out whether your frog died from a pathogen, I'd be very hesitant to simply jam another frog in there, anyway.
You'll have infinitely better results by researching a species, and then setting up an enclosure tailored to the needs of that particular species. A dart frog enclosure is nothing at all like a white's tree frog enclosure, for example, and showing up to an expo and buying whatever catches your eye there (choosing on the basis of color isn't at all a good way to choose a captive) isn't a recipe for success.
Good luck! Frogs are interesting captives.
