A proper set up in a 25 gallon tank may only leave enough room for one. You want length to provide enough space for landscaping and available territory to house more than one and you may also want some depth to create a DSB or plenum to culture denitrafying bacteria. These animals will also produce a little more waste than other reef fish, so creating a DSB or plenum can help control a heavier waste load of nitrate.
A DSB will require critters that crawl through the sandbed to release trapped hydrogen gases that accumilate from the denitrafying processes. The gases then dissipate into the atmosphere and completes a full nitrogen cycle. You'll need at least a 4" sandbed for this to work. Being denitrafying bacteria are anaerobic, they need an oxygen deprived environment to thrive. The deeper the substrate, the more weight placed upon the bottom layers, choking it of oxygen. In reef predator tanks, you can find great benefit with having bristleworms...with or without a DSB. Not only would they keep the sand sifted and clean, but provide the means of releasing hydrogen gases from a DSB without being preyed on.
A plenum is a substrate divider type thing made with a PVC pipe framing a strong plastic grate wrapped in screen mesh. It is placed on top of a 2" to 3" layer of substrate and then covered with another 3" or more of substrate. Problem with plenums is they may trap small digging fish under the grate like jawfish, shrimp gobies and their shrimp, and also eels. If you do not plan on having these types of animals, then a plenum is fine. Plenums provide a dead space for denitrafying bacteria. The screen mesh wrapped around the strong grate helps reduce oxygen from all the water activity above the top layer.
Training a predator taht relies on movement to take in dead food takes patience and a little creativity. Prepare yourself to go fishing in your tank...LOL. Sort of. Use a feeder stick and pierce a thawed out piece of krill or a silverside on the stick. Make it move past him as if it were swimming on by him. Sometimes, if you have good aim and the current is right, you can let these items of food swish in the current of the tank over them. The food just needs to move in a way that is natural to the species to strike out to the food. You just need to supply the 'mechanics' for this food to move.
