How many plants do you need to put in an aquarium to make a
significant dent in nitrates?

We all know plants use nitrates as a food source, but I have 4 potted
plants in my 20-long aquarium and the nitartes do not seem to be any
less. Is it that I need to put a truckload of plants in there to
reduce the nitrates or what?

Right now only my monthly water changes do anything, and I'm not
looking for a way to stop doing water changes, it's just that I don't
want them getting too high because it promotes algae and is bad for
fish.

Frost