I set up a 10g just to see how well some plants removed the nitrates. It has 2 red mangroves and every inch of the surface is stuffed with water lettuce. I started with just a few lettuces, but now it's a carpet. There are no fish. Each week I drain out about 1/2 - 2/3 of the water and replace it with the water from my CA tank water change. Afterwards the nitrates in the 10g measure about 10. By the next water change the nitrates are at zero.