Thanks again for all of the responses, this feedback is AWESOME!
I would still try to plan for a lower water level, you don't need the extra 10 gallons in your sump, and it won't make a big difference to capacity. I am assuming you either have an overflow or an emergency drain of some kind in your main tank? What happens if your tank is filled to a point where your emergency activates and then the pump stops? How many inches of water do you lose in your main tank? 1.5 inch drop is enough to overflow a 15 gallon empty capacity in this setup.
- The main tank has dual overflows (one on each end), so if one clogs there is a backup. There is also the protection factor that the pump supply segment will run empty if I stop getting overflow -- meaning I can only pump an extra 5-10 gallons in there. I get your point that you probably don't need the extra capacity down there. Let me drop it another inch or two.
I would also change how you have your mechanical media. Currently you have it being stacked on top of each other vertically. Change it so they are stacked horizontally. This means you can pull one for cleaning without disturbing the others. You may find that your fine clogs quicker then the other 2 for instance and rather then pulling all 3 you could just pull the fine one as needed.
- If you turn them sideways, wouldn't they have to go the full width of the tank and height of the waterflow? I think that could work if I removed those baffles and just used a big egg crate section to have sideways flow. Is that more or less what you would do for freshwater? Could potentially be interesting. I was just thinking that if I'm rinsing / replacing filter pads I'd cover the whole stack.
And then... why do you have a refugium? It makes sense in saltwater tanks but we don't really use them. For instance, you REALLY do not want a light on in this cabinet all the time. Unless you just love cleaning algae off of glass. Instead it should be dark down there unless you are servicing the sump. If you need a storage area or grow out location for plants a separate tank is a much better option, it doesn't even need to be a tank, a plastic sterlite container works fine. And if for whatever reason you really really really want another compartment down there, your return pump doesn't need to be 11 inches wide, something like 7 inches is more then enough. And definitely look into the size of heater you need for this tank.. cause 13" is probably still too small.
Agreed, it's not necessary for freshwater since you don't have things like skimmers or ATS in there. Since I had the space, I like the idea of having it for acclimation or to isolate a bully fish (agreed, you could do that in a separate tank). What would you reclaim that space for? Side note, a 40 breeder is 17" wide, so there's plenty of room for heaters long ways in there.
Do you have any plans / photos of sumps you've done for freshwater? I'd love to see the arrangements.