They like high humidity which requires damp soil. Both Springtails and Isopods do good in a wide variety of soil types. ABG mix tends to be the best because it has so many different comp nets to it and will break down slower. ABG mix when cared for properly can last for over a year before it need to be replaced.

Isopods do the same job that Springtails do and can be eaten by the frogs as well, though most frogs prefer to eat the baby isopods as they have a softer shell. Having both Springtails and Isopods will not cause harm to one or the other. Having them both in the terrarium helps in bring as much of nature as possible into the habitat.

I know it is in another thread here, but refresh me on the frog you are putting in here. I think it was a Dart frog, they require high humidity which will lead to the soil being moist but not swampy which will be perfect for the soil insects.

From your picture in the first post I don't see any leaf litter. Your frog will love leaf litter. It gives them loads of hiding spots if they get spooked. It will lead to your frog being more bold than it otherwise might not be. NEHERP has leaf liter as well. Its cheap and you will get more than you need. Save what you don't use to add in after a month or 2 and to replaces the leaves that have decayed.