depends on which kind of wrasses, the fairy type you can keep as many has your tank can hold, as long as there are not 2 males of the same or similar looking one
I have 2 Canary Wrasse (Halichoeres chrysus) and a Solar Fairy Wrasse (Cirrhilabrus solorensis) in my 90g reef. I had 1 Canary for over 5 years. A few months ago, I saw the Solar Wrasse at the LFS near work. After watching it for a few days, I couldn't resist and took it home. It got along great with the Canary. A few weeks ago, something spooked the Canary & it jumped. It bounced hard of the center brace. It sorta floated down and disappeared into the rocks. After not seeing it for 2 days, I picked up a new small one at the LFS. Ten minutes after adding the new Wrasse to the tank, the original came out. They've gotten along great since.