I am going to change over to a 75 from 56 gallon. I am wondering if I can add Marinepure blocks in the sump instead of sourcing more rock for the tank. What if I stacked 2 of them on top of each other so I had a 8x8x8 block? I just want the function of 10 pounds of live rock. All my LFS have are man made rocks or some that look like rocks from my backyard and I dont want to mix that with the rock I have accumulated over 10 years. My parameters are fine so I am not trying to get anything down. I just want more filtration appropriate for the tank volume.