Min 10gallon tank per frog is recommended. Tree Frogs prefer to climb so a tall tank preferably atleast 24 inches is ideal. Make sure the food you are giveing is smaller than the width of its head to prevent blockage. I feed mine a strict diet of crickets dusted with calcium and the odd house fly we happen to catch. Your temp looks good make sure your humidity levels are proper as well and always clean water.

If you havent already, read the Care sheet on Grey Tree frogs in is amazing and has lots of info needed to raise a happy healthy Grey.