I got two 10" iridescent sharks a week ago and they're not eating. I tried feeding them sinking shrimp pellets but they ignore it and swim past it. Other tankmates are two 8" Oscars and a 9" Pleco. The Oscars don't bully the sharks at all, and the pleco hides under it's bridge ornament. They're in a 72 gallon tank that has good filtration. I know its not a tank problem because the sharks came from a 55 gallon tank. Please help