would a single blue acara be able to live comfortably in a tank of this size, and will it be okay living by its self, or will it be shy and not come out.
This is roughly a 33 USG tank...Blue Acaras get to be 10" max...I would not attempt to put the Acara in this tank, or I would be prepared to do excessively large amounts of water changes as the fish reaches full size...and I would not go for any tankmates unless you want to do more water changes!
There seem to be multiple blue acaras. I had found 10", but, for the one most commonly called by that name, 6-8" is what I am finding. 8" would imply a 40 gallon (~150 L).
If the acara is young it should do ok in the tank for a while but it will grow to around 8 inches and ideally should then be moved to a bigger tank
They are not generally a shy fish.
Cheers
you should be fine with 1 blue acara in a 33g/125L tank.
as for the size of them they will get roughly 6-8" with the max being 10", after they reach a size of about 3-4" they will grow slowly, it is said 6-8 because that is the size most blue acaras seem to get. 10" seems to be for people to hope.