Dead Amazon Milk Frog

I had an Amazon Milk Frog, Quazzi, who just died.He was a family favorite, and I am very upset over the death and I am looking to find out what happened to try to prevent anything like this from happening again. He was in a 12x12x18 enclosure with a similar sized red eye tree frog, although the two were never active at the same time and could care less about each other. They have been in the same tank for a few months, and Quazzi was around a year and a half old. His tank was set up with a mister that would go on at 6am and 6pm every day for around 15 seconds to keep the humidity high. The bottom of the tank was coconut fiber covered in frog moss. He has shown no signs of illness, aside from a birth defect that made his hip jut out the wrong way,although he still moved around just fine. I have never used any cleaners or chemicals around the tank, and hes had plenty of crickets with the occasional dusting of calcium. Temperature is room temperature, and the hygrometer says the humidity usually stays around 60-80%. A few months ago it did look like he had almost like a blue gel coming from his but, although it went away after a little while. Yesterday he was hoping around chasing crickets and this morning I saw him face down on the floor dead. Please help? Any ideas? I want to make sure the rest of my amphibians stay fine.

Just a thought, I could be completely wrong here, but the deformed hip and the fact that the calcium supplements were only occasional makes it sound like it could be metabolic bone disease?

I have a limited knowledge of tree frogs, but I'm guessing that metabolic bone disease is a possibility..? It's worth researching. Also, as a general rule, it's best not to house amphibians together, no matter their temperament. If you get another milk frog, it would be best to get a second enclosure.
The blue gel sounds very odd.

Temperature may have been part of the issue. Unless it was at least 76F during the day, then 'room temperature' is highly unsuitable for this species.
It also may have picked up an illness from your Red Eyed Tree frog (a reason not to house different species together).