Quick Question on downsizing tank

[CodeMan28]

Im downsizing my tank and i was wondering should i use new sand or old sand, or should i mix new with old. I know with freshwater you would use some of you old water. Im guessing its the same for saltwater too? i have never downsized with my saltwater tank.

Any and all help would be awesome thanks

 

[EllieSuz]

Old sand can pollute when it gets disturbed. I would recommend you discard your old sand except for a cup or two to "seed" bacteria in the new sand. The only advantage in using old water would be parameters would be identical in both tanks. If you have high nitrates in your old tank, mix old water with new saltwater half and half.