Sump are much easier than they look to be honest. All your doing, is creating a place to house your filtration equipment, along with, if you choose, a place to either have a second mini display/incubation area, a fuge for algea, plants and micro fauna growth, or, a frag growing station..
And someone can correct me if I'm wrong, but in its most simplistic form(which I prefer personally), is just a holding vessel of some type, with baffling to achieve the water heights you wish in each area.. Lol, nothing really complicated. It's when you look at more elaborate sump, that it gets confusing (if your not familiar with sump design..
I have had sump systems on tanks from 10,up to my current 180. And it's simply because of the ability to increase water volume and equipment. There really isn't a time "to me" that I wouldn't use one, unless I couldn't. From topping off, to water changes, to the ability of better skimmers (in sump design are much more numerous and traditionally better performing), to adding supplements/etc, to simply not having your system looking like a science fair project "all of the time"(lol, mine looks like nasa, and I like it that way, in my cabinet, but to the outside world, it's very calm and serene..).
I build very simplistic, but functional 3 chamber sumps for myself. They focus on length to allow good flow, but with emphasis on skimmer/overflow and fuge sections.. And it's very, very simple honestly.. I just think about my return pump and is height.. That, plus an inch at least will be the minimum water level in the return section (because, you don't want them to run dry or annoying bubbles). I then, think about two or three pumps in that minimum area, and the widest plus an inch is usually how it works out, but this section is usually the last thing I worry about, and it just works out.. Then, with bubbles in mind, I always, set my skimmer and overflow (filter sock area on the opposite end. That allows the water to flow nicely, getting rid of all the bubbles beefier the return area.. I also, make this section a priority in the sense of size, because this is the area that I will work on the most, along with the most equipment.,so it needs to be roomy and comfortable. It also, sets my skimmer water height. I base both around 9", as most current skimmers have that somewhere in the middle of their operating range.
The fuge or middle area, because I grow cheato, I like that big.. So, with the long or breeder series tanks, it works out great..
I also, always set my baffles at only a little over the height they need to be.. I have this fear of never having enough "legroom" in case of power outage by the baffles being set to high..
But with those basic things, all you need, is a tank (preferably for you sized display a 20 long or I can't remember the size for my 50,but it was 36"long, and almost the same width and height as a 20 long), a couple pieces of glass for the baffles(3 pieces, see my little pic), some silicon, and 24 hours to let it cure.. Very cheap and rewarding endeavor..
As you get comfortable, you can get more elaborate of you wish.. But I keep them simple and just increase size when I can.. And just remember, a few inches added in water level height for your return and middle section, adds a significant amount of gallons..
Oh and this is the same design, just instituted on my current tank. The sump is a 75 gallon that adds (though it doesn't really look it) 35 gallons of water to my overall total water volume..
