What size tank is the shark in? How long has it been set up and what are water params for ammonia, nitrite, nitrate, and pH?
Water quality will have a huge effect on appetite, as will stress (poor water quality will add to stress levels). Also, try feeding when the lights are out, they tend to be nocturnal feeders.
My guy eats flake food just fine, but he waits for it to sink to the bottom and won't eat if the light is on. I've had him for about 2 yrs now, an orphan that I took in. He's about 5 inches long now and has a 40 gallon planted tank all to himself. He's a happy fish, healthy and colorful!
If you're putting all that food in the tank and not cleaning it out, its very possible that your water quality is not so good right now, which would cause him to still not eat. If you do water changes, do lots of small ones, 10%/day, doing a gravel vac each time to get the food out of the gravel. When you get to 10% of the water, stop, and pick up where you left off the next day, etc etc. This will keep your tank and fish healthy without any risk of shock from extreme changes all at once or loss of beneficial bacteria.
