A Volitan in a large tank can easily reach 14 inches in length. However you will not get one to continue to grow in a tank that small. The big problem you will have with a large lion fish is filthy water as they love to eat and poop. Some people over rely on carbon with large fish populations. It is not a widely accepted practice and is done only by the few. I would definitely use a skimmer with all large fish , especially predator fish. I have kept lots of Volitans in the past, even before the widespread use of skimmers. Skimmers were pretty pathetic back in the seventies, powered by just wooden airstones. The typical tank had crushed coral for substrate and an undergravel filter, and no live rock. Volitans will accept some prretty dismal living conditions and survive, but that does not mean they should be subjected to that now that reefing has developed beyond those practices of years ago. I would recommend a skimmer, a deep sand bed, sand a good load of live rock and buy a young small lion fish. As the deep sand bed develops you will be able to remove more and more of the live rock supplying room for the Lionfish's growth. I would limit carbon to an as needed basis only just to provide water clarity, not as afiltering media for fish wastes in general. Use it for a few days at a time as needed. Another good alternative is a trickle filter or a bio wheel and no deep sand bed or live rock. Without corals you do not need to worry about the higher nitrate level you will have. You will mainly need to control the nitrates enough tp keep from having algae problems. Trickle filters and BioWheel filters are great for fish only tanks. They are the most effective nitrifying filters in use today. They are much better nitrifiers tan a deep sand bed or live rock. However nitrate levels are nearly always high with biowheels and trickle filters making tem a poor choice for atank with invertebrates and corals in aprticular. Still limit your carbon use to an as needed basis with either a biowheel or a trickle filter.
