probably about once a year . . . I keep a lot of plants in my tanks, and I like to give them time - - say, 6mos to a year - - to grow in before I decide if somethig works, and if it doesn't work, then I will re-do it
I did re-arrange one of my tanks recently because the pair of Port Cichlids I have spent way too much time hiding . . . I was trying to encourage them to come out more . . . results were mixed