Shall I add start adding coral(s)?

[Katze]

I'd just let them be. Sometimes coral take a while to adjust, especially to a new tank.

3-4 months ago my rastas thought that they will close for over a month (it must be mentioned that po4 and no3 were sky high) at the end all died, that's why I'm worried. So just patience for now and the two of them will open up better?

 

[Lavey29]

3-4 months ago my rastas thought that they will close for over a month (it must be mentioned that po4 and no3 were sky high) at the end all died, that's why I'm worried. So just patience for now and the two of them will open up better?

Patience is key but also ensuring water parameters, flow and lights are all in sync. Stability is they key to success in this hobby.