My cleaner shrimps are hiding

[specrn5]

I have a couple of cleaner shrimps and they used to be so active, especially around feeding time. But recently they've been hiding between the rocks and the back of the tank. They both molted not too long ago, so I don't think they are preparing to molt. I haven't changed anything and the parameters seem fine.Though I did add a fairy wrasse last week, but it doesn't seem that he is bothering them. I dunno, any ideas on what is going on?

 

[iCam]

They will generaly hide after molting until their shell hardens.