:lol lol, by "mate" I meant friend, sorry for the confusion.
Yes after the frogs are put back in the 6g, their tank can be cleaned (not with soap) and used for a QT. PLease make sure Dopey is well and all meds removed before putting the froggers back. Glad you have 0 ammonia now. Sorry I can't remember, are you cycling the 6g? If so, make sure its completely cycled (no nitrites and less 10 nitrates) before adding the frogs back in. With two adfs and a tetra in the 6g I don't think you have much room left for more fish. If the tetras are small, then maybe you can get two more. I am not sure if its good idea to just get one more tetra. They may pick at each other, but the FW experts will be able to help you make a good decision.