I don't have the tank I want to use as a sump yet, but that doesn't stop me from thinking about how I am going to put it together once I get it. I've spent a lot of time looking at other people's sumps, but as with everything (it seems), I feel the need to tinker and make my own design.
In this particular case, what I want is the ability to install my Aquaclear 50 hang-on-back filter on the sump itself. This will give me this ability to keep it cycled, in case I need to use a cycled filter in a QT tank. It also will assure me that the filter is still working; I have found that pumps have a tendency to stop pumping if left dry and unused for too long. Putting it on the sump and not on the main tank will keep it out of sight.
This means I need an area of the sump where the water is close to the top of the tank. This is not a feature of most sumps, as you generally want a lot of extra room for the water that flows back down into the sump after you turn your pump off. So my area of high water, ideally, needs to be fairly small. This is what I came up with:
(The design has a grid that's meant to be roughly 2-inch squares, but they are not exact. For instance, I probably won't have the water level a whole 4 inches down in the high-water bit; it will probably be more like 1.5-2 inches.)
The water will flow down from the tank into a filter sock, which is made out of a fine material to catch all of the solid waste. Ideally, these are changed out very frequently (some people do it daily) to take the waste out of the tank before it turns into high nitrates. From here, the newly un-gunked water will flow through some ceramic filter media (I wrote biomax here because it's shorter; I haven't bought it yet and may well end up with a different brand), which functions better when it's fully submerged. After it does that, it will go back up and over a ledge into a drip tray, which will spread the water out and sprinkle it through a series of small holes over a basket filled with bio-balls, which are plastic spheres with ridges that give a lot of surface area. They work best when they are wet but not submerged (which is what the wet-dry in wet-dry filter refers to). I plan to have about 5 gallons of these. After the water makes it through the bioballs, it'll fall down into the bottom of the sump, where it will be pumped back into the tank by the pump I wrote about here.
Here is a side view of the sump design, which shows where I will put my Aquaclear.
I'm not sure how close to this my sump will actually end up being. My projects have a way of changing while I am making them. But this is what I'm shooting for.