Can I use a certain filter media specially for nitrates?

[Sunpoe]

a wet dry filter that has 4ft to 6ft of media will break nitrates down.. i do understand many can not afford such a filter

Really, I was always under the impression that anaerobic bacteria where the organism that broke down nitrates, in such an oxygen rich filter it must be by some other means. Could you possibly explain this further or point me to a website?

Thanks