There's "will it physicall fit", and there's "will the fish be able to swim around comfortably?" A silver will eventually hit 3' in an aquarium. So 6'x3' would be 1x width and 2x length. Nope for me. At least go 8'x3'.
Silver arowana tank size?
- Thread starter Fishnerd360
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The good news is you have 10 yrs to save & plan for a larger tank. 
Appreciate the comment, similar situation as op but the UK doest have similar laws to the US from my knowledge.
I'd say 8'x4' min. for a silver or black arowana. If you are wanting 6'x3' go with a jardini. Add him last and make his friends be bottom dwellers with enough places to hide. Even with my tank at 8'x4' I'm going to upgrade as it is too small IMO for these stunning elegant fish.
There are alot of shapes for a 380. Imo anything less then 8'×3' and at least 20" deep is to small. So if you take 96"×36"×20" = 69120 cubic inches now ÷ that by 231 why? because there are 231 cubic inches in a gallon so that = 299g
So as long as those 81 gallons increase length width or depth beyond those measurments then perfect.
So a 96*36*36 inches would be a good tank size for one of these silver arowana. Right now a 6*2*2 feet seems more likely in the coming future, so what tank mates can be with jardini's, can any mid dwelling fish live with them? Or only fish like rays, bichirs, and plecos and other catfish?
Bottom dwelling fish will be your best chance. Give them plenty of low cover to stay out of the jars sight. Plecos would probably do alright, holding their own and a tougher catfish. Mid level is probably out unless you get that super rare jardini that doesn't become a homicidal mad-man at 12". With any monster fish, you run the risk of tank mates being killed. As I mentioned previously, if you get a jar add him last after the rest of the tank has been there.
96×48×24 would be better but yes that would work.
As for tankmates anything is a gamble. You could get an uber aggressive jardini and it'll kill anything that's in the tank. You could get a skittish jar and it will spook and slam the tank or jump out and die. You could get a jar that tolerates bottom dwellers only or one that is fine with anything that's not (insert whatever color here). So many variables. It's one of those things you will have to try and see. I've a "friend" that got a jar and it was fine until it got to 12" then it killed everything it had grown up with. A guy at the lfs has a large almost 24" one with a bunch of stuff in a pool including a silver, its fine also wont eat anything but pellets (none of that is normal). I have never owned one so I can not tell you exactly how or what will happen from actual experience, but neither can anyone who has owned one. They are all different.
As for tankmates anything is a gamble. You could get an uber aggressive jardini and it'll kill anything that's in the tank. You could get a skittish jar and it will spook and slam the tank or jump out and die. You could get a jar that tolerates bottom dwellers only or one that is fine with anything that's not (insert whatever color here). So many variables. It's one of those things you will have to try and see. I've a "friend" that got a jar and it was fine until it got to 12" then it killed everything it had grown up with. A guy at the lfs has a large almost 24" one with a bunch of stuff in a pool including a silver, its fine also wont eat anything but pellets (none of that is normal). I have never owned one so I can not tell you exactly how or what will happen from actual experience, but neither can anyone who has owned one. They are all different.
