Short answer is make sure it can accomodate the water volume when the returns are off. I originally used 1" random flow generators on the return lines and had to put them deeper into the tank to avoid sucking air from the surface. When I turned off the returns, I did not have sufficient volume in the sump to hold all the water backing up. As a result I ended up having to reconfigure the return line going back to the tank and ditched the random flow generators.
If the sump is going to be out of the stand, you'll have more freedom with size. Will your sump be in or out of the stand?
In my case, the sump measures 66x20x15. When I turn off the return pumps, the water now fills to within a few inches of the top of the sump. That's adequate, but I think the more room the better. My display volume is approximately 330 gallons and with a larger display this would definitely be a consideration. Here's what it looks like with the drains off for a minute, it would fill up a bit more if I gave it a little more time before snapping the photo.
The 15" height makes it easy to work in the sump, and having easier access to the sump in the stand was important. If the sump will be out I would definitely add height. In the stand, I'd consider going to 16".
The 66" length was the max I felt I could accomodate while leaving some working room on the side of the tank. I made a little diagram at the time anticipating how I was going to lay it all out. I ended up putting the the trident in the back of the tank and nixed the electronics cabinet when I routed all the electrical to the closet behind the tank, so perhaps could have gone longer. It is nice though to have room around the sump in the stand. I like room in the front of the sump too, but could simply have gone deeper to add water volume.
Here's how I have the sump layed out, and some more detailed thought reflecting on each section.
Drain | Mechanical Filtration | Skimmer | Dual Return | Reactors | Refugium
I have two filter rollers in series. I don't like socks but I know many who don't mind them. The filter rollers work, but occasionally will roll up on an angle. Then I have to play with them to get them rolling back in line, and this happens maybe once a month. Not sure if the new red sea roller design may be better. This is not too big of a deal for me, and they've worked and spared me having to deal with socks which has been a plus. More importantly is the consistency for the system of having the mechanical filtration changed. I would put off changing socks (still do) in my smaller tank.
I do run the first roller on a timer while the second runs off the float. I do this to maximize the rolls, otherwise I was going through the first roll much faster. I end up using about two rolls for the first roller a year and 3-4 rolls for the second roller a year. So 5-6 replacement rolls a year between the two. The filter rollers turn off when the returns are off as well.
The skimmer chamber was built to fit the foot print of the Bubble king Deluxe 200. If you decide to go with filter rollers, undersize the skimmer. But this chamber can be adjusted to fit whatever skimmer you select. I ordered my skimmer and return pumps through Geo as well. He built lids for each chamber, but I don't use them.
The return section was also sized to accomodate the specific return pumps I selected. If you have larger return pumps, then this section would need to be bigger.
Each return feeds one media reactor that then puts water out back into the skimmer section. I like the integrated reactors because it's tidy and easy to swap out media. The schedule 80 fittings are not necessary for function, but I like the quality for unions I'm opening and closing regularly. I use one reactor for GFO and the other for carbon.
The refugium is post returns. We sized the return and skimmer sections more tightly to maximize this section. The water gets fed to this section off of a manifold from the returns. With occasional die off of chaeto or from other sources, I still get detritus in this section. Not a big deal, and easy to clean. I don't get coralline in the other sections which is a positive of the form factor of this reefbrite light.
If I ever implement a calcium reactor (the first thing I purchased for this system), I would send the effluent to this section. I have thought about the best way to stabilize pH when using a calcium reactor. I'm not sure whether it would have been better to simply have the water move through the refugium passively post skimmer and have effluent go to the skimmer section to blow off CO2 prior to going to the refuigum where more CO2 would be utilized by the macro algae. I don't know the answer to this, but something to consider.
For the returns, the outlet of the return pumps is 1" and I went to 1" plumbing. I believe you have less friction loss from the returns if you upsize the plumbing. Not a big deal as I have more than enough power in the pumps, but simply a more efficient way to plumb. The one inch plumbing carries up all the way to the tank and in the tank I split to 3/4" loc-line.
