Hi Griffin,
Although I have red eye tree frogs, I am not an expert.
However, here are my thoughts.
He is thin, and looks weak. I am glad that you were able to do the soak.
PM Grif and ask how often you can do that?
It is stressful for them to be handled , though!

If this were my frog, this is what I would do for now :
-I would keep him in a hospital tank to monitor things closely. ( 5-10 gallon glass tank $ 10 )
-get what ever is needed, ( lights heat etc to keep this separate tank)
-paper towels substrate.
-add a pothos vine or a plant he can climb on and hide in
- cover the back and sides of the tank with dark paper.
-keep him in as quiet a spot as possible
-dampened the towel w/ declorinated water ( change it 3 times /week ONLY while he is sleeping)
-include a VERY shallow / soaking dish w/ the same water that the paper towel is dampened with ( change it daily ONLY while he is sleeping)
-*****Keep the temp and humidity w/in the parameters recommended ******
-keep a very consistent day/night light cycle
-dust crickets ( small ONLY- make dinner an easy catch ) with vit D and calicium **** DAILY****
-put several crickets in - every night ( count them !!!)
-remove ALL uneaten crickets in the morning ( after he goes back to sleep ) put them back in the cricket bin to feed
-Light - I would hang 2.0 UVB bulb near-by during the day ( maybe 6 hours /daily)

You are sooo consciences !! Hang in there!
Lynn