What type of lighting? From my experience with my Rainbow monti's they can take some time settle in. Also they prefer intense lighting and high flow. If polyps are green or faint orange/red usually that's not enough light. If polyps are yellow/orange its the right amount of light. Also the base should be bright blue if the lighting is right. Otherwise it may be faded or dull looking if lighting is off. I found it doesn't care to much about parameters. As long as they're pretty stable you should be good.