New to reef tanks

Hello everyone,

I am new to reef tanks and have purchased a 36 Gallon tank. I put all the rocks (3 dry rocks, and 4 live rocks) from my local store. I set the tank up and got the salt correct and a few weeks later I purchased two tomato clown fish and some snails. I bought a reef test kit and when I tested the water the calcium was at a good level but my dKH was extremely low. Is this because the tank is new or do I need to do something different?

Thanks.