[G1GY]

I would keep all of the original water in buckets with the livestock ect. Then maybe wash the new substrate very well (with warm tap water.) and rinse it in some dechlorinated water, put everything back in the nano just as you planned and just go realy light on the feedings for the first two weeks. Regular testing of paramiters will let you know if you have a spike on the way, but I don't think you will have a problem.

I've done this with other tanks with no ill effects, but nothing that small. (The smallest I done this with was 33 gallon.