Pictus Catfish & Plecostomus question?

I have ^^^^ those fish and I know the plecostomus eats algae, and when I bought the catfish it said it ate tropical fish flakes. I bought Tetra Color Fish Flakes... When I put it in there neither of them notice it they just keep swimming. I don't think they have ate the 2 days I've had them. Could someone tell me what I'm doing wrong, I don't want them to die.