Don't buy any dart frogs yet. They are not aquatic, but live on land with plants. While you can put in waterways, such as streams and waterfalls, these are superfluous. I'm not sure how to begin helping you from here.
You should hang out on the forums, do searches, read care sheets, and get a good understanding of what dart frogs are, and the general biology of frogs before you attempt to keep any as a hobby.
There are many species of dart frogs, and they live in rainforests, mostly in South America and on the Islands. They are terrestrial, and don't live in water or swamps, but still require some small collections of water to reproduce. Some species live high in the trees among bromiliads. Others may live on the ground. Most require temperatures between 65 and 80 degrees F. Most like high humidity, between 80 and 100 percent, and temperatures between 65 and 80 degrees F. They are diurnal-- active during the day.
You might tell us what species of dart frogs you want to get. It might help us to help you if you could tell us something about yourself, such as your age, where you live, etc. That would give us an idea of where to begin to answe your questions.
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Patty
Pahsimeroi, Idaho
4 D. auratus blue
5 D. galactonotus pumpkin orange splash back
5 D. imitator
6 D. leucomelas
4 D. pumilio Bastimentos
4 D. fantasticus
4 P. terribilis
4 D. reticulatus
4 D. castaneoticus