It depends. You have to have a way to get water from the tank to the sump, and from the sump back to the tank. Some sumps come with 3' hoses(s) to carry water from the tank to the sump. If not, you'll need a hose for that, as well as a hose to carry water back to the tank. Does the tank have an overflow on it? If not, you have a couple of options. You can drill a hole in the back of the tank with a diamond dust hole saw and install a bulkhead, and another hole for the return line. Or... you can purchase an overflow box that hangs on the back of the tank, and one of those return nozzles that also hangs on the back of the tank. You'll also need a return pump to go in the sump. Since it's a small tank, you won't need much flow through the sump, so you'll need to get a pump that matches the flow... since the pump is what determines the amount of flow. Sumps are typically designed for a skimmer to sit in the large chamber, but they aren't completely necessary. You can put some filter media in the large chamber, and it may be all you need. A pantyhose bag with ChemiClean and another with carbon will do a lot for cleaning the water if put in an area of high flow. It's possible to put macro algae in the big chamber if the flow isn't too strong. Since it's only a 20 gallon tank, and sump flow should be around 10x the tank size, a 200 GPH pump should work just fine. That should be the amount of flow going into the tank, not the pump size... so something like a Mag Drive 2 would work nicely since it pumps 205 GPH @ 3'. I was typing when you posted that you had ordered it. I was hoping to get this posted before you ordered it, in case it looks like all the accessories might be more than you want to spend on a sump. There are some HOB sumps and/or refugiums that will work fine for a small tank, and don't require alot of the stuff needed for a remote sump.
~beaming~
