There is nothing that you can add to your tank to decrease anything in there. Conservation of mass, right?
Whatever you add may well convert it to a different form that doesn't show up in the tests, but the nitrigen is still there, plus you've added some other substance to your tank.
If you want to decrease NO3, or anything for that matter, water changes are the only viable long term solution. Anything else is just a stop gap. All those adsorption media or reaction chambers will only server to decrease over the short term. If you're diligent with media changes, you won't have any problems. If you're not, you'll run into big troubles when the media expires. Even if you are dilligent, you're just spending extra money.
IMO, all those products out there to get rid of this and that are for lazy fish keepers who don't expect to keep fish for very long. As RTR pointed out in your denitrifier post, all you're doing is removing the compound that lets you know how much other biological, um, biproducts are in your water.
NO3 is not your enemy, it's the stuff you can't measure that comes along with it.
