i think i break all the rules in the book....
i kept them in a 20 gal tank (24x12x17) with 1 sponge filter (hydro sponge 4) and plus 2 airstones in it. (do not even dare to ask how many was in a 20 gal--way beyond what you can imagine is what i can say).
keep feeders all the time, a lot of them--and feed the feeders as well because they will try to bit the armatus due to hunger (i have seen this already).
now they are on a 48x15x12 (custom tank). about a handful of them with 1 sponge filter (same as the one i used for the 20 gal tank) and 3 airstones.
i personally have them always on bare bottom tanks (easier to clean), but they do acted weirdly when i first introduced them to bottom tanks.
this is only my advise, do not over do your fish or it might have chronic migraines from the wirlpool in the tank.
but having more filtration is good..just don't make them spin all over the current.