What to do after fin rot?

Hello,

I have just lost white cloud mountain minnows to fin rot. I am guessing
that this is because the tank had not been fully cycled. Now I am more
clued up on the cycle, etc, what would be the recommmended course of action
to take? - take everything out, wash it and start the cycle again, or leave
the water in there that the minnows were in and keep an eye on water
chemistry until it completes the cycle?

Thanks