Spotted marsh frogs

Hi all,

I have a question about my 2 beloved spotted marsh frogs of 7 years old, as they seem ill. I am very worried about them.

I am from Adelaide, South Australia and I got given these 2 male frogs 5 years ago from a friend (they are from the wild, from around Adelaide) who could no longer take care of them, because she was moving interstate. She had them for about 2-3 years and gave them to me in their big beautiful tank. They have always been very healthy, eating well and calling loud at night. I feed them crickets and supplement these with calcium (repti-cal from aristopet).

However, in the past week their behaviour has changed a lot and I believe that they are ill.

Here is what happened:
I recently introduced a female spotted marsh frog (that I got from a friend - he caught it on his farm 40 km from here, so it was wild also) into the tank. I fed all the frogs crickets and all seemed fine. Sadly the female frog died after about 2 weeks. I found her sitting at her usual spot, but she was dead. I found her when she had just died, and she looked perfectly fine, well fed and all. However I examined her a bit more closely and I found a tiny caterpillar like flat worm-like animal on her leg. This freaked me out a bit so I cleaned out the whole tank (the same was as I normally do).

I though everything was fine, however, 2 weeks after this happened my 2 beloved male spotted marsh frogs have suddenly become very lethargic, they are not eating and their skin feels very sticky. They look bloated as well. They are not hopping as they used to do (instead they are crawling) and they are also not hiding under their rocks as they usually do.

I am not sure what to do, but I am worried that they will not make it if I do not take action.
I can not see anything abnormal on my frogs, there is no red skin colouration, not slime, no marks or anything, and no parasites on the outside of their body. They are just very slow, and they feel so sticky, which is a big worry.

Does anybody know what might be wrong with them? I have read a lot about disease and parasites, but none of the information I found mentioned anything about sticky skin.
What can I do to help my beloved frogs get better? Any treatment suggestions?

Hope you can help! Any advice will be much appreciated!

Many many thanks!

M