Space in the aquarium stand severly limited the size of sump I could run so this is my constraint. I am also needing the return pump to be very quite as the DT is in our bedroom.
How big of a return pump do i need for my sump - The Reef Tank
You also must take into account your aquarium equipment when deciding on the size of your sump. One of the biggest perks of a sump is that you can hide all of that unsightly aquarium equipment in the aquarium stand. When designing your sump, make sure you have room for all of your equipment, including gear, like protein skimmers, reactors, heaters, secondary filters and pumps. For example, protein skimmers and calcium reactors often have tall bodies, and you must make sure your sump still will fit into place with these large pieces of equipment.
What size return pump should I use? - The Reef Tank
Some hobbyists use their sumps as refugiums. Refugiums consist of a separate tank that includes some animal, plant or algae connected to the main aquarium. For example, some sumps contain a refugium for algae that can absorb nitrites and ammonia, which that fish would devour if they could get to them. Some refugium designs may limit the size of your sump. If you plan on growing copepods or other tiny crustaceans in your refugium, you will need to plumb the sump back to the main aquarium via gravity drain, since a pump would shred them. This usually means you must have a smaller sump, so you can mount it above the aquarium.
I have a 65 gallon tank with a 20 gallon sump
In order for water to flow to your sump filter you've got to have some way for it to exit your aquarium. Canister filters use pumps to suck the water from the aquarium and then return it back again. Although sump filters utilise a pump in the system, this is only used to return the water back to the aquarium, water exits the aquarium using gravity. There are various different ways that you can set up an aquarium so it can house a sump filter, however, one of the more common ways is to use overflow boxes. Overflow boxes are normally installed inside the aquarium. Depending on the size of your tank, you can either have one overflow box installed or two. If you look at the simple diagram above you can see that this illustration shows two overflow boxes located at the rear of the aquarium. The white circles depict where the inlet and outlet pipes are located. The overflow box is designed so it's not quite the height of the aquarium glass, it needs to be like this so that the water flows freely into the overflow box like a weir. The water then flows through the inlet pipe and down into the sump filter, it is then returned through the outlet pipe. When you switch your pump off, the water will continue to flow into the outlet box until it drops below the lip of the weir, at this stage water will stop flowing out of the aquarium. There really isn't any more to it, this is how water exits your tank when using an overflow chamber or box. However, one of the drawbacks with using overflow boxes is they can be very noisy. If your aquarium is located somewhere where you spend lots of time then the sound of flowing water could well get rather annoying after a while. There is a simple solution to this problem and it can be resolved by using standpipes. You can either make them yourself, or you can buy commercially available pipes. When you locate standpipes in your overflow boxes, the water then backs up until it reaches the point where it will start flowing through the standpipes. Because the inlets on the standpipes are located near the top of the overflow box, the water doesn't fall so far, in fact you can set them up so the water only needs to for a couple of inches, this will dramatically reduce the noise the water makes when dropping, in fact it can cut the noise out altogether.