Well this was in a biocube 14g, so it was easy. I literally filed a 5g bucket with tank water, then put the LR in the bucket, then threw out the sand, and the rest of the water and put the new sand, put in all the LR the way I like it, then filled with 50% old tank water, and the rest new water. If it's a big tank, then you're basically screwed lol.