2 frogs dead and one frog sick!!!!

2 of the RETFs were around 3 years old and 4 around a year old. They have all been fine and eating and acting normal. 2 days ago I found one of the 2 year old frogs dead. Yesterday one was moving around during the day quite a bit and was walking around almost like he was drunk, very uncoordinated looking. This morning I found him dead. Now today I come home and one of the 4 year old frogs is sitting eyes WIDE open during the day and about 50% of him has faded to a pale green color and another year old shows a little sign of discoloration and he just looks uncomfortable.

What in the world could possibly be going on here? I assume some kind of virus/bacteria? Only 2 changes to the tank recently. 2 weeks ago I andded some springtails. 4 days ago I added one of those bendable vines to grow a vine plant on, Is it likely one of those additions coould have introduced something harmful to the frogs? Is it possible crickets can introduce something?

I'm just a little frustrated. The frogs have been doing great for 3 years and now I seem to be losing one a day.

I'm the only one that touches the tanks so I am sure nobody cleaned it. I did not ask if the springtail culture came from a frog tank but I probably should have. I assumed they didn't. I got them from the show in Hamburg a couple weeks back. Maybe it was that bendable vine I just put in? How would I go about making sure something like that is clean before it goes in the tank?The good news isthe 2 sick ones are still alive and showing signs of improvement. They are moving around and their skin seems to be clearing up. They still are obviously sick though but at least looking better.