you will get mixed reviews on this. Check out my thread in this section on page 2. "just got a Purple Firefish". My LFS would tell you no, but it has obviously been done. I was told one per tank. This site says they do best as a pair or group of 3. I will tell you this, once I get a second DT set up, I will be purchacing another whether its Purple or regular, and if it does not work, I will have a second tank to put it in. I think its worht the try. Mine stays in his rock most of the time and darts into it when fish swim by. Those behaviors make me think that a second wopuld be fine, they would either keep each other company or have sepaerate rocks to live in.?