I agree with Patty on this. I would would like to add a few things.
First off , there should not be a great deal of fighting in a tank. If there is this means that you have too many of one sex. Females will fight with females and Males with males , in some species. If you see alot of fighting , take one out.
Darts are amphibians and can hold there breath for an extreamly long time. Drowning has come up before in other forums and I have not heard of one single person who has ever watched a drowning. Not hard to beleive. It is always someone who heard of, knows of, or has a friend who knows of, a drown frog. Think about this. About the only way that a Dart drowning could be doccumented would be a study with cameras going around the clock on a tank with fighting frogs. I am guessing that nobody on this board or elsewhere has actualy watched while their frogs killed each other by drowning, especialy since this would take the better half of an hour, at least. If I am wrong I would definatley like to hear the story. There could have been studies on this subject but as of now no-one has come foreward.
I have talked to a number of froggers who have questioned frog deaths. It would seem that many times a frogger finds a dead Dart it is in water. I theorize that this is because of a drive to either re-hydrate, or an internal need to seek out or be in water when there is something wrong with the frog. I beleive this to be true because when talking to people who have found frogs dead in the water they were paired frogs that do not fight. Murder was not an option.
I think that it is imortant to have a water feature. It is a good idea to try to have an keep an easy way of exiting. I do not think that there are many (if any) Dart frog drownings
though.
One last thing about water features. For those breeding "picky" morphs. The water feature can be as deep as you like but for some morphs you will want smaller Brazil nut husks, film cans, broms, something that holds smaller, calm , amounts of water , in addition to the main feature. Frogs tend to not want to deposit their tads into torrential water features. They do not do it in nature and do not like to do it in a viv.
I hope this helps.
Rich