They are easy... Provided they are healthy.

would you please describe what was happening, where did you buy(get) them, did you quarantine them? Have you treated and what did you use? What type of water have you used? How this sphagnum look like ( long stings/milled)? What size of tank did you have for these 6-8 frogs? How old were these frogs?

Answering these qs might help to point out something.