Well I moved on to the second mock up. Total dimensions are 48 x 22 x 16. Total of about 75 gallons. This is shorter than the first mock up but only about 5 gallons less in volume. I am liking the 7" filter socks for easier cleaning and now thinking of placing this sump under the tank instead of in the basement. The refugium is approx 17x22. This is the area that I want to be as big as possible and from looking at other sumps this seems like a good size.
Seeing this I have a couple of thoughts... first, the partition after the large middle section is way too low. Not only will it keep the water level in your fuge and skimmer sections very low, but it will significantly decrease the overall water volume in your sump.
Furthermore it will decrease the water volume in your return chamber as well. You want as much water volume as you can get in the return chamber (within reason) because that is where the water level will drop as water evaporates. If you don’t have an ATO that means that you’ll need to top off the tank very frequently or risk the return pump running dry. If you do have an ATO then it gives you a very small safety margin in the event that the ATO fails or you accidentally let it run dry.
I would try to raise the overall water level in the sump as much as you can.
Second, the second partition in the return chamber really isn’t doing anything. The return pump sucks the water from the bottom of that section anyway, so it’s not really going to function as a bubble trap. I would either remove it entirely or add a third ‘over’ partition so the water from the fuge goes over, under, over to get to the return pumps. That would be a much more effective bubble trap.
One thing that I did when I designed my sump was to make the water level in the filter sock chamber and the skimmer chamber as high as possible and then make the water flow over a partition between the skimmer chamber and the fuge where the water level would drop a bit. This allows the water level in the skimmer chamber to remain at a constant level whether the return pump is running or not. When the return pump is turned off the backflow fills up the return and fuge chambers, but the water level in the skimmer chamber is high enough that it is not affected. This prevents the skimmer from needing to be turned off or overflowing when the return pump is turned off.
Finally, I used glass for my sump, but I made the partitions on either side of the fuge out of dark smoked glass. The dark color helps prevent a lot of light from leaking into the other chambers in the sump and helps prevent algae from growing outside the fuge chamber.
Overall though it looks like a great sump design and I think it will do well for you
