A remote sandbed is basically just a super cheap way (comparatively) to get the denitrification benefits of a deep sand bed with far far less risk: you can simply remove it at any time if you need.
Basically all it is is a 5gal or larger bucket almost completely full of sand (round and argo works best, but cheap sand is just fine) which you plumb into your system by having some steady flow over the top of the sand and then it drains out again, again from the top. The point of the flow is simply to be strong enough to keep any detrituts from settling on the sand, which would just make the sand a nutrient sink (and thus not last as long or even become a nitrate problem instead of solution). Diffusion does the rest: the water spreads throughout the sand i the bucket (hard to believe for some people, but its inevitable) and gets dinitrified in the low oxygen environment, then leaches back out into the water on top.
That's it. No lights (definately no lights: you'd grow diatoms and other nuisance things). No macro algae. Nothing special at all. Again, the flow is simply to keep any detritus from settling. You are not trying to pump or push water through the sand. It will diffuse on its own.
It's a very cheap DIY: probably cheaper and easier to maintain than a coil denitrator. All you need is a 5 gal container (or more, you can even use a spare tank if you have one) like an old Instant Ocean bucket, a weak ass powerhead/water pump (you'll only need about 140 gph or even less: you may have to dial it down with a ball valve even), plumbing supplies like bulkheads if you are going to drill into the bucket, and then the sand. And maybe a lid (since a 24/7 dark environment is best). That's it. Most people have all the supplies for it just sitting around.
Search for plans online.
