It depends on what kind of fish they are. For instance Oscars are mainly "top feeders", if it sinks to the bottom my Oscars don't see it until I point to it at the bottom. My Severums hang at the middle and grab it as it falls, Platys stay at the top and don't check the bottom til the top food is gone, etc. So I guess it'd depend on what kind of fish they are and what level those fish normally eat at.