My folks are happy to get a larger tank if I it comes to that. However it would need to be about 2 years down the road. Do you think the flowerhorn would have any stunting or hunchback issues in the mean time?
Your fish will not be stunted by your tank size ime. More often stunting is a product of poor water quality.
30-50% water changes weekly will be a good routine to stick to. However, If you are feeding heavier, dont be afraid to double up on changing water as well.
On that note, be sure to feed a varied, healthy diet for your flowerhorn. Include vegetable based pellets as well as high protein foods.