A modest gradient for a small frog
Green tree frogs are not basking animals in the way a lizard is, and their gradient is correspondingly gentle. During the day the warmest corner of the enclosure, high up near a low-wattage heat source, should sit in the low to mid eighties Fahrenheit. From there the temperature should ease down through the high seventies in the middle of the enclosure to the low to mid seventies at the cool end, where the planting is densest and the water dish sits. At night the whole enclosure can fall into the high sixties or low seventies, a drop these frogs expect and handle comfortably. The total spread is only around ten degrees, but the frog will use every part of it across the day, climbing toward warmth after feeding and retreating to the cool leaves to rest.
Why the cool end matters as much as the warm end
A small frog loses moisture quickly, and heat accelerates that loss. The cool end is where your green tree frog protects itself: shaded leaves, damp substrate, and a clean water dish kept out of the lamp's reach so the water stays cool and inviting for soaking. If the whole enclosure drifts warm, the frog has nowhere to slow its body down, and chronic overheating shows up as restlessness, refusal to feed, and long spells soaking in the dish. Keepers sometimes chase warmth for an inactive frog when the real problem is that the enclosure offers no genuinely cool, humid corner to feel safe in. Build the retreat first, then add gentle warmth above the opposite corner.
Creating the gradient without cooking the enclosure
Use the smallest heat source that does the job. A low-wattage basking bulb or a small ceramic emitter over one top corner, outside the mesh or behind a guard, is usually enough in a room that is already comfortable for people; many green tree frog enclosures need heat mainly to lift the warm corner a few degrees above room temperature. A thermostat keeps that gentle lift from becoming a spike on a warm afternoon, and its probe belongs near the frog's favourite high perch, not down at the substrate. Place a thermometer at each end rather than one in the middle, because a single middle reading hides exactly the gradient you are trying to verify. Misting raises humidity without adding heat, and the leaves under the lamp dry fastest, so check that the frog's warm perch still offers nearby cover.
Reading what the frog tells you
Your frog's behaviour is the final check on the numbers. A green tree frog using its gradient well moves around the enclosure across the day, calls and feeds in the evening, and changes resting spots. One that spends all day pressed into the coolest, dampest corner may be telling you the warm end has crept too high or spread too far. One that sits constantly at the very top under the lamp, dark in colour and inactive, may be too cold overall or unwell. Frogs that stop feeding for more than a few days, lose weight, or show skin changes need a veterinarian with amphibian experience rather than another adjustment to the thermostat.
Keeping a narrow range steady
A ten-degree gradient in a small glass box drifts easily with the weather outside it, which is why the checks matter more than the equipment. KinsLe's Care Teams suit this rhythm, because the morning warm-end reading, the evening cool-end reading, and the water change can each sit with a named person, and every completed task is marked with a timestamp, so a slow drift upward gets noticed in the record rather than guessed at.