Why 40lbs of sand?
I worry that your gonna have to much flow thru your sump and the sand is gonna end up all over the place.
One of the principles of a sump is that you can remove equipment like heaters and powerheads out of the main tank. Well to remove powerheads you have to provide a good source of water movement. To do that you need to get a sump pump that will give you this.
A flow rate of 1
the water capacity of your main tank is recommended to a 55 gal
tank would shoot for 550 gal
per hour of flow rate. When sizing pumps also have the head height measured. Find a pump that gives you atleast 1
flow rate at the head hight between yoru sump and the top of your tank.
If your wanting a refugium then maybe a 20 Long tank would do better for your sump. You could section off the sump to have a small area with lower flow for the refugium and then part of the sump for your heates, skimmer and the higher flow of yur sump returns and pump.