Sand. Bare bottom tank cycling is different than ones with live sand. It’s not as straightforward as you might think. Especially when starting with dry rock. I understand that you are adding some live rock to boost the cycling but still…cycling a tank with live sand is easier and more stable. Plus bare bottom tanks look more like store displays than a natural reef in your home. Cleaning sand is a ***** but I got the ehiem vaccuum so that helps me. I have a 120 gallon, yeah it’s smaller than your set up but is by no means a small tank. If I perform cleaning on a regular basis I’m good. Plus I added a tiger tail cucumber and some conches. They help out too.