if you're running the tank you have to add a source of
ammonia for any bacteria to establish. you can use either pinches of flake food daily, a piece of raw shrimp, or pure ammonia (shouldn't bubble or fizz when you shake it, just ammonia and water, and no surfactants). unfortunately the used tank water won't help since hardly any of the beneficial bacteria is housed there, you'd really just be adding ntirAtes to your tank.
yeah, i'd probably go ahead and just get a new one, who knows what's built up on there.