Minimum 100 litres clear water tank required for succesful grooming a Flowerhorn fish to full potential (150 litres to get the best outcome).
Every 7/8 days 30% water change with good quality water, you can siphon the ground poops too during the water change.
Try to keep a constant temperature of 28 to 30°C and also do check that there aren’t any drastic changes in the temperature during water changes, for which you can keep off the thermostat before 12 hours of water change to acclimate with the new water.
Try to add some natural gravels (pebbles round shaped small size) and few ceramic rings(white/red) to maintain a good quality of water and beneficial bacteria.
For a FRY of 1 to 2″ maximum 6-8 pellets per day is enough (dividing the total number of pellets in 3 to 4 times a day), for juveniles of 3″ to 5″ maximum 16-18 pellets per day is enough (dividing the total number of pellets in 2 to 3 times a day), for adults of 7″+ maximum 30 pellets per day is enough (you can also increase the number of pellets only on fish health and if he wants more max to 40 pellets).
Not necessary to use more than 2 or 3 foods at the same time, try to keep one basic diet food like (okiko, hump head, probio, amber, etc) and one high end food like (amg, cz, farmhouse, etc).
You can also feed blood worms but keep it concentrated to maximum 2 or 3 days in a week.
Flowerhorn fishes normally stay active most of the time, so no need for extra mirror training and all but you can always give parrot training every day for 10 minutes maximum if you want to.
Try to understand what your fish needs and when does he stays happy most of the time, try to treat your fish like your friend, he will treat you as his friend too