I literally surround nursery froglets with food, feed juveniles and breeding frogs daily and go by what Josh has just said, otherwise. Some people put a small piece of fruit in the tank in order to test whether flies are still present, but usually you can spot some roaming around. Tincs and azureus are fairly active frogs and do eat a lot normally. Pinheads are a great treat, but except for thumbnails, I keep them for about 10 days and let them grow a bit (on some grain and vegetables) before feeding the larger frogs.
Recommended supplements are alternating Rep-Cal and Herptivite. I like Tree Frog Dust (T. Rex.) I also use Dendrocare, ostensibly formulated for darts, but it seems to have too much vitamin A in it, unless I'm confused somehow by IE units (which I don't know what this is) and IU units (International Units) which most formulas use. Vitamin A can be overdosed unless it is in the form of Carotenes. I also supplement with a scatter of paprika which contains B carotene, which can enhance the color of some of the yellow/orange/red frogs and can also be converted to vitamin A only when the frogs require it, so can't be overdosed. I dust every feeding because I scatter the flies and the powder rubs off a lot of them before they are captured. The vitamin powder also helps control the flies so they aren't swarming all over the feeding cup. However, I think most dart keepers dust only every other feeding or perhaps 3 X's a week. In any event, your dusting formula should contain both calcium and D3, because cultured fruit flies and crickets are low in calcium and most dart vivariums get no UV light for the conversion of D vitamins to D3, which is essential for the utilization of calcium. This is an over-simplified explanation, but the idea generally works.
You can see if your frog becomes fat and waddles--then cut back. Otherwise, a short period of being "portly" isn't fatal. A lone frog may be prone to overeating without having to work hard and compete for supper.
That IS a good looking frog.
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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