Sooner or later you will get eggs. Usually you will get a couple of clutches of eggs that will go bad and mold over. This is normal. Bad eggs will swell up and get cloudy. In developing eggs you can actually see the tadpole develop in the egg. When I get eggs, I take a paper towel, wet it, and place it in the bottom of a 24 oz Ziploc container. I then take the Petri dish and place it on the paper towel (I do not put the top of the Petri dish on Petri dish). I then add enough RO water to just touch eggs. If the eggs are laid on a film canister, leaf, or on the side of the tank, I scrap out the eggs and put them in a Petri dish and add water so it just touches the eggs. Finally, I put the Ziploc lid on and mark the top with species of frog egg.
For more information on taking care of dart frog eggs, please watch the following video: