I would say just continue keeping an eye on it and get a pic if you can.
I will also say that the heating pads are totally useless and more of a danger to your frog than help. If your frog gets cold, it will dig itself into the ground closer to the pad and possibly burn itself. You temp range is a little high for a white's. I keep mine between 74-78 during the day and 70ish during the night.
Also, the suggestion to get a bigger tank is worth listening too. These frogs can get fairly big and if they don't have the right size enclosure, it will not get the exercise it needs to live a long and healthy life.
If you are worried about humidity, try some real plants, they are great for keeping the humidity up. The first thing I would do though is get rid of those heating pads (I may have mistaken, but if there is one against he window, they can be deadly to the frogs, as the frogs cannot tell when they are getting too hot.)
If you do decide to change tanks, get rid of the spagnum too. Bad for impaction. Just use the bed a beast, or coconut husk. I have several plants in that that are doing just fine. THe bedabeast also holds the water in, so you won't have to water the plants as often and it helps with humidity. I would put in something for the frog to climb as well, like wood, rock, jungle vine, flower pot. Anything. they love to climb.
Hope this helps a little.
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I think my frog owns a megaphone....
White's tree frogs : 1:1:0
Mantella viridis : 1:1:2