You need to purchase some test kits to see where your tank is in regards to it's nitrogen cycle. Ammonia, pH, Nitrite and Nitrate. You can read here or any other reefing website how best to determine when to add your first inhabitants.
In the meantime have a closer look at your rock and I bet you will find lots of critters emerging.. feather dusters, crabs, polyps and pods to say the least. Don't forget to have a look again about an hour after the lights go out.. lots of cool nocturnal crawlies.
You do not need to do water changes until you tank is in "production".
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