Acquaclear makes good hob filters, but I think you're under filtered based on your current bio load. I think that a 55 gal tank is a bare minimum for a fully grown oscar by itself (messy eaters); the snakehead only complicates the problem. I'd suggest moving one of the fish to another appropriate tank. On my 55 gallon stocked with a poly senegalus, poly palmas palmas, clown loach, and 2 africas cichlids, I do 2 50% water changes a week to keep the nitrates in line. You may also want to limit the light as previously stated for a while to help inhibit algae growth.
