You don't want water to go through the sand and disturb it. There are many creatures that live in the sand that would rather it not be disturbed, especially in a fuge. Plus, if you disturb the sand there is a good chance that sand could get in your return pump and damage it.
Also, check to make sure you are going to have enough room for "run off" water when you turn your pump off. It looks to me like your baffles are extremely high and that there isn't a whole lot of room for error when it comes to having enough room for run off water. Measure how much space you have left in inches LxWxH and divide by 231 to get gallons that are left for run off water. Then, calculate the gallons of runoff water by measuring LxWx2 / 231 to get how many gallons of run off water there will be. If it is close to the same difference, or you get more run off water from the display than what is left in the sump - you will have to cut down your baffles. I always try to leave at least 2" from the top of my sumps as room for error.
Just trying to help.
