how long has the tank been cycling total? Did you use cured live rock when you started? If you started from scratch meaning new rock , new sand , new water it takes a good 30 days to cycle a tank . I start all my tanks this way. and even after 30 days and everything tests zero , I only add a small clean up crew couple of hermits a few snails. feed small amount of pellets every other day to get that nitrogen cycle going. after about 2 weeks and everything is still testing at zero you can add a hardy fish or an easier coral that you like . your tank will be a "new" tank for months even when you are able to start adding things so going slow is the best bet.