I am trying to give myself a buffer for water changes. Right now ammonia and nitrites are stable, and nitrates rise as expected. I'd like to know what other steps I can take to reduce the rise inn my nitrate levels.

I have seen these star things which are supposed to drop into the filter, but I'm pretty sure those are for the ammonia and nitrites, as bacteria that eat nitrates don't grow in oxygen rich waters.

I have a 20 gallon long planted community aquarium with a log, a few porous rocks, and an emperor 400 filter (big sale). I'd like to know aside from the plants, what else can I do to reduce nitrogen levels? I'm not trying to eliminate water changes.


You basically have 2 options to control nitrates in any fish tank, fresh, salt, or brackish: reduce nitrate introduction (stocking and feeding), or increase nitrogen removal.

The only realistic way to reduce nitrates without water changes in any fresh or saltwater aquarium is through anaerobic breakdown which occurs in anoxic (oxygen free) environments. The problem in a tank this size is that there is virtually nothing that will remove nitrates that is anywhere near cost effective as water changes as it's almost impossible to create the environment that anaerobic bacteria can exist. Even in a 100 gallon freshwater tank it's almost impossible.

Generally speaking there are a few non-water change ways to reduce nitrates:

  • Deep sand beds
  • Large low flowing ceramic or other filtration blocks
  • Sulfur denitrator filters
  • Coil denitrator filters
  • Algae turf scrubbers
  • Algae or plant refugiums
  • Carbon dosing (vodka, vinegar, biopellets, or other), but this method is arguably ineffective in freshwater as it normally requires a protein skimmer to work effectively.

Realistically in a 20 gallon tank, none of these would be remotely worth the cost compared to figuring out an aggressive water change schedule. It would likely take years of operation of another method to break even compared to even daily 100% water changes.

  • I would also add using aquatic plants in the aquarium to the answer. Though most prefer ammonia, some would use nitrates mostly, and for others that prefer ammonia, with little ammonia and nitrites, they'll probably use the nitrates. This link should clarify: www.theaquariumwiki.com/Plants_and_Biological_Filtration – Mozein Oct 27 '14 at 4:11
  • @Mozein yea, i'd assume the biological filtration would remove most of the amonia, so they'd have to take N. – ton.yeung Oct 27 '14 at 5:17
  • Would you mind adding some descriptions on how these various filters work? I tried googling the first few and got some very jargon heavy sites. – ton.yeung Oct 27 '14 at 5:20
  • @Mozein in a 20 gallon tank, you can't stock enough vegetation and a deep enough substrate for either to be effective enough. – jwenting Oct 30 '14 at 7:55
  • I'm not sure about that, in a 20 gallon there also is less wastes due to less inhabitants so not much filtration is needed. I've seen many planted 20 gallon tanks and I don't think the toxic substances removal by the plants was something you can nullify. You do have a point though, in larger tanks, plants probably do have more of an effect. – Mozein Oct 30 '14 at 14:50

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