Jardini Arowana get to about 24-30"+ in a well filtered tank and a 180 gallon is a good size tank to keep these in =] But be warned though they can turn on your back once hitting the 6-9" point as at this point they become killers and become mighty aggressive but thats only in most Jardini's not all are mean as they can be kept with others but with Very High Precautions must be made as having an extra tank just incase if you do want tankmates...but they are spectacular when grown up Try your luck with these guys
yes this is true My last jardini arowana was in my family for over 4 years and was about 29" That was back a few years ago... but then he passed away into the new big watery tank in the deep blue sky above us Darn it...he was shocked to death when we had a black out for only 20 minutes but then when we got the power back the heater busted and i guess got to his poor little heart