Sick Tomato frog, any help will be appreciated.

[Mentat]

Thanks for your replies.
1. I dust the frog's food with repashy calcium plus almost every feeding.
2. Yes, the sick frog is pooping, but I have never gotten fecals done for the frogs.
3. I use tap water to prepare the coco fiber, but I usually let it sit for a couple of days before adding it to the tank. I change the substrate about every 1-2 months or somewhere in between. I spot clean and change the water daily. No, I have never gotten the water analyzed.
I have a spare 20 gallon tank that I could set up for better monitoring. What should I put in that tank? Thanks for your help.

Sorry missed your post, been under the weather last few days. Thankfully Colleen/Jerrod and Lynn took care of it. It's OK to use aquarium de-chlorinator although would avoid products with skin conditioners for fish. ET Aquatize, Seachem's Prime, etc. are all good. If Spring water leaves marks on glass can use distilled water for misting and spraying enclosure (not for water dish). Good luck !