They have been kept successfully in a 55 but the concensus of ALL briareus keepers is that a 65 should be the
minimum recommendation (unlike the mercatoris dwarfs no maximums have been suggested
). Look through the Tank Talk thread for equipment suggestions. Off the top of my head, a starter list, with each item needing thought, would be:
Tank (prefferably drilled for a sump connection using a bulkhead). We have found that tanks having a 2" or more lip at the top and lowering the water level between 1 and 2 inches from the top seem to be a major aid in dissuading escape.
Stand (with room at the bottom for a sump and built to take the weight of both)
Secure Top (extra security important for briareus)
Skimmer (lots of skimmer discussions in the sticky at the top of the Tank Talk forum)
Live Rock (1-2 pounds per gallon -pricey)
bottom substrate (I recommend crushed argonite about 1" thick)
power heads to circulate water (octo safe. We like and use the Koralias but others have mentioned problems with stray voltage)
RO/DI unit to filter tap water, OR source for RO/DI water and salt mix (not a trivial expense). Even if you buy premixed water, you will need fresh RO/DI water for daily evaporation top off
Additional Filter (sock with charcoal/wet dry cascade style unit/canister)
sump (I recommend 20 gallon as a minimum - tall tanks are nice for this use to be able to have some depth and still have room for the back flow of water when the pump is off.
pump to return water to the tank (another expensive item)
optional lighting if any kind of corals are to be kept in the tank
optional red ligthing if you wish to watch night time activity (briareus are active at night)