Thanks guys,
It is about 2" from peak of the rocks to the inside. Some are 4".
I cut a 8ftx4ftx1" down into strips (2" and 4" pieces) Home depot graciously cut it at the store for me so i knew it was nice and straight. From there, my wife and I cut the pieces down to fit and to look like rocks. That took a few Saturdays to get done.
I never thought about the cracks being an issue. I have this running plumbed into a 375 gallon so I will have roughly 850 gallons. So hopefully there is enough volume to counter any issues of any junk getting stuck in the cracks.
I plan on putting white sand down as well. Still trying to decide on the kind. I may try some bead blast sand. Otherwise I was looking at caribesea torpedo beach. I wanted the white tile down as it always bugged me when my rays would move the sand and I would see the dirty plexi underneith. This way when they move the sand around I still see white.