I have a Rio 400 which holds the same amount of water as the Vision 450 which used to be home to a tiger Oscar. I did want 2 oscars in it but a 5 foot 450 litre really isn't big enough to house 2 oscars. I know have a single thai silk flowerhorn in my rio 400. Iv tried a few different fish with the FH which include a jack Dempsey, Oscar, red devil and a buttikoferi (all bigger than the flowerhorn) but the flowerhorn just killed them all
Anyway, all I did in my rio was as I stated above... I just bought 2 x 18 inch long air stones, a couple of plastic clamps to even out the air flow to both stones and some plastic tubing. All from my LFS (local fish store) then I ordered an air pump online. Just make sure the air pump you purchase is rated for the tank size you have. The 1 I bought is the tetra aps 400 (pumps through 400 litres of air per hour) that was more than enough for my tank.