Welcome to Simply Discus Masonmnieland
It's very common when a group is transferred to a new home they are skittish at first and now one week later they are developing a pecking order and it appears the one in the group as you mention has became the loner. Adding some furniture like plants or driftwood will give the loner somewhere to hide but in most cases it all works out in the end as they grow.
I will question why your using R/O DI ?
...Ralph