Hi Daniel, you've received a ton of good advice above. All of those questions when answered will go a long way quickly to answering your question. I think I know exactly why your frag isn't expanding but your answers will help us help you.
There is a sticky above entitled " when asking for help". It is vital that everyone provides as much detaild info to receive a swift and helpful answer.
1. Your tank looks really new, is that true? If so, as OG stated, how old is it? Possible NTS.
2. Is that coralline algae on those new rocks and on the subtrate or just a reflection?
3. Before you take any corrective measures...take a look at a thread I posted in this forum entiled, " 25 reasons why your polyps won't expand". Please check it out. If you can't find it...I will post a link.
4. How long has that frag been in your tank and was it purchased locally or was it shipped?
5. I agree with Organism, if that is ornamental plastic and not inert, it could be leaching.
6. What is your tank temp?
Reactive dipping is great if warranted, but I'd wait a minute as all dips are stressful albeit some are more than others and could exaserbate your polyp retraction.
Good luck.
MUCH REEF