u should start thinkin about that tank very soon. with an armatus's growth rate, mine only lasted in a 140 for about 7 months. the bigger they get the more aggressive they get. u are probably sick of hearing this but im only telling u from experience. its a ticking time bomb. my armatus was ok with many tankmates b4, until he snapped. i have seen 2 armatus in the same tank but the owner said u need alot of space. his tank was over 1100gal. their are alot of armatus owners on this site that will tell u the same. its not that its too risky, its that it wont work. i would'nt listen too other people when mine was small, then he started killing. im rely rely rely gonna hate to say i told u so.... im sure you've already seen some aggression between them. its gonna get worse and worse.