A 12X12X18 would keep a pair of azureus very well. When you get confused about spelling azureus, think of "azure" - like azure skies--a lovely shade of blue. The others you are thinking of are probably Dendrobates auratus, which come in black and green, blue and green and other shades. They will all survive well on fruit flies alone, but other foods are always welcome, and give some variety to their diets, as long as it is alive, moving and small enough for them to eat. Dendrobates azureus in the wild actually subsist on more springtails than other things. Springtails are very easy to culture, but are small compared to fruit flies. Pinhead crickets (the newborns between 6 days and a couple of weeks or so old) are also a nice source of food, and most darts love them. I have used rice flour beetle larvae on occasion, but find them a PITA to separate from the rice flour. Some people use small termites, but I have no experience with these, and others may use certain ants. In using ants you really need to be careful and know the various species, because some may be more dangerous to your frogs than the frogs are to them. The small so-called pavement ants and sugar ants may be a food source for darts.
If you have a garden that is free from pesticides or live in an area as I do, which is a rather large ranch where the pastures are never sprayed and no chemicals are used, with an organic garden, so called "field plankton" is a nice source of dart food in season. I run around in summer with an insect net and swoop up tiny critters from the grass, trees, etc. for the frogs. They love leaf hoppers, gnats, whatever is small enough to go into their mouths. They particularly like a fruit tree leaf full of aphids-- or any aphids you find on other plants that haven't been sprayed. You can just remove the leaf with the aphids and place it in the tank. And no, it is very unlikely the aphids with infect the live plants in your tank, for several reasons I won't elaborate on here. But they won't. Isopods, such as baby pill and sow bugs get eaten, and it is safe to put a few adults into a tank to see if they won't produce some frog food. In my experience, they don't prosper for long, however, and raising them in boxes is more effort than it's worth.
In any event, you can feed a lot of different live insects as long as they are pesticide free, but do need to keep basic cultures of fruit flies for the main diet, along with some springtails, perhaps-- expecially if you ever intend to feed newly morphed out tadpoles.
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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
2 D. azureus
4 P vittatus