Yes you are correct they went from their old nitrate infested and phosphates infested water too basically a new setup again. I was instructed to do this by the aquarium store I go to (a marine biologist who I've gone to for years who's never steered me wrong) who said years of high nitrates and phosphates have leeched into my live sand and live rock and to just go ahead and start the setup over again.
He said water changes could be pointless at this point as each time I would do a water change the phosphates and nitrates would just go back up from the LR
and live sand leeching it out back into the water.
I tried the best to get their old water to match the new tank water but I gave up and just hoped for the best and in they went back into their home! They're doing great and look so happy and active to be out of that nitrate and phosphate infected water.
Yes he did say cycling might be an issue but said with the live sand, live rock and skimmer going, lots of extra water an prime in case of an ammonia spike everything should be ok.
He basically flat out said unless you get these parameters down you'll never be able to add anything new again! On top of that I felt bad because what kind of pet owner am I to leave them in nitrate and phosphate infested water over the years?
So... the first battle is over.... now it's on to monitoring water parameters to make sure I don't lose them from a bad cycle. Wish me luck!