that will work you have to prep him like training him like week by week like lowering the temp in the tank as low as you can get without filteration but do it very slowly dont rush the oscar or it will be fatal. I have actually preped my 12 inch oscar that i wanted to get rid of because he was such a problem for me. I have a creek behind my house and its not small im talking about 20 miles untill it hits some larger bodies of water. and every week i would take 10 gallons from the creek and pour it into a 40 gallon i had him in for training and i would lower the temps by 5 degress every week and if the water wasnt cold enough i would go to the creek at night and get 5 gallon ands drop it in there. the creek water is not clean at all so this was a huge change for him. i live in maryland, around the edges between md and va you can find oscars/ snake heads in the waters but the snakeheads are being put out by anyone who catches them, but your not doing creek water ne ways, so i made a rock divider that he can not get past or back the other way and it is about 10 feet long from divideer to divider and no hiding spots, so i can check on him, but its been about 6 weeks and hes still there. its about in the 50-60degress here at night maybe 45 n up but its getting colder and colder i dont think he will survive the winter. but your way will work just train him they are hardy fish.