Replacing Sand in Established Tank. Will it Cycle?

[Alabamareef]

Had an major issue in my tank, that's not the topic, and this has me thinking about replacing all my sand and starting over. Left in my tank are some tangs a couple of clowns and some chromies along with a cleaner shrimp. Also have 4 RBTA and 3 BTA. One of my SPS friends has suggested this. I know he up sized his tank and we replaced the sand but added some of his old water back in and it never seemed to cycle.
This is a 180 gallon system. I want to save about 40 gallons of old water and everything else will be new, water that is. My question is will the tank go through a cycle like a new tank or will I be able to add back in my animals after we get it put back together?

 

[Saltgator]

Are you gonna siphon the sand out or scoop it out? I'm currently removing mine, but 1/4 at a time. I'm going BB. I'm only doing 1/4 at a time to allow the system to accept the change gradually.

Country Boy using tapatalk on his EVO

 

[Russellaqua]

allow the system to accept the change gradually.

This is the key. If you replaced everything at once you'd definitely get a cycle. All sand, where "live" or dry, is going to have some organic material in it that is going to decay in your tank when added, so that will be a small cycle. Your old sand might also have a lot of old detritus/gunk in it that will be stirred up when removing it. This can also cause a cycle, the severity of which depends upon how dirty the sand is. Removing and adding only a small amount at a time helps reduce the severity of the cycle. I might do even less than 1/4 of the sand at a time, just because I like to err on the side of caution.

 

[Alabamareef]

Just curious how my friend managed to put in new sand when he upgraded and all his fish and SPS did fine.