he is talking about taring down his tank and scrubbing it and then refilling it. I think it is not nessasary to do this. If the white stuff is ammonia scaling then all he needs to do is siphon the scale as he scrapes it off the wall. ammonia scape will draw in ammonia as it is prodused and release it slowly you can do all the water changes you want and it will not do much to corect the problem phisical removel of the scale is best option. But lets see what the tests come back as. A CA scale will also absorb ammonia and release it in to the tank.

by the way a massive water change can shock the fish faster than finding the cure of the problem and resulving it. He is running carbon and a protien skimmer. treat 1 thing at a time and you can help to do that by doing smaller water changes, and he has moved his fish from the problem tank which also gives him more time and yes he can now do a larger water change.after he does a good cleaning of the tank glass and sand bed vacume the sand bed realy well. Now is the time to do it while the fish are out of the tank.
Bill