I had the good fortune of limited access to an ichthyologist and marine biologist who operate an LFS here in Southern California and work at an aquarium in San Diego. We began what became almost a full year of informal but largely quantified gatherings of data on nitrate reduction techniques and efficacy. Some is unfortunately anecdotal but much of it was quantified in a way that some Aquarists may find helpful.
Filtration options for nitrate reduction, can be difficult, expensive and surprisingly fragile. The aerobic bacteria consume ammonia and nitrite, the anaerobic consume nitrates...but the latter are fussy eaters! Nitrate reduction via filtration often has little to no effect as
it can take 6-8 months to build a sufficient anaerobic colony to actually reduce nitrates meaningfully...and this requires enormous volumes of media.
Far more than would be need for the rest of the nitrogen cycle!
We began cultivating anaerobic colonies in pond media and found the amount of media required for an efficacious anaerobic colony to be far greater than we hoped for or that would be practical. Nitrate reduction via anaerobic colony filtration is VERY inefficient and requires voluminous amounts of media for meaningful nitrate reduction.
One example being a massive 900gph canister filter with some 6L of media capacity and TWO of these filters with a total of 12L of media, still cannot support enough media for effective anaerobic colonies for a ‘typically stocked 125G cichlid tank’ for significant nitrate reduction.
One such filter has ample amounts of flow and media capacity for aerobic colonies (the bacteria that removes ammonia and nitrite), but for anaerobic colonies (the bacteria that consumes nitrates), you’d need FOUR such canisters (25L pond media or similar) to have enough media to reduce nitrates just 10PPM!
I also find anaerobic colonies are MUCH more fragile than aerobic such that they are easily killed by accident. I cannot quantify this but I have experienced the results and I’ve yet to successfully neutralize rechargable media well enough to
NOT reduce the anaerobic colony count.
In fact, re-using rechargable (with bleach) media that was then soaked in dechlorinator for 24 hours still killed off almost 6 out of 8 months growth of the anaerobic colony! Yet the aerobic bacteria saw no drop in population.
(I believe Pond Guru mentions a similar test and results in some of his videos)
I went a different route after months of trying to get meaningful nitrate reduction in the filters. Instead of trying to get nitrate reduction with more filters or additional media, I tried Epipremnum/riparian plants: roots in the water, leaves out the top.
I replaced part of the glass with plastic lighting grid to support the roots and stalks:
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I had initially added Epipremnum/riparian plants primarily because I thought it was pretty. I had NO idea the degree of nitrate reduction this would have. I was not prepared for the results.
One tank was a 120G heavily stocked with adult, SA cichlids, 12 Acaras, 2 large plecos and 8 Severums in this case:
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A 2nd tank, a 125G was heavily stocked with larger fishes, plecos, Oscars and pacu’s (I’ve since had to rehome my beloved pacu’s as they were approaching 18″ in length!):
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The following are before and after a two week period with Epipremnum/riparian plants above in these tanks:
-The 120 typically reached circa 40ppm after a week when I’d do a WC.
-Inside of two weeks, the 120G at 40ppm has yet to ever reach 10ppm.
-The 125 was more problematic with nitrates I was having enormous difficulty controlling. This tank (prior to rehoming the pacu’s) would typically reach 80ppm-160ppm inside of 1 week (!) such that I was performing 2-3 WC’s/week until I could rehome them!
-Same time frame, the circa 80ppm-160ppm tank had still not risen to even 30ppm!
There was also little question that the nitrates fell further still once we installed
grow lights. This is not shown in the pictures as they were not installed yet;
-With the lights on 12-16 hours/day or so, the 120 dropped from 10ppm to 5ppm, or possibly 0, it’s that difficult to read.
-The 125 dropped to 10ppm and has yet to ever reach 20ppm since adding the grow lights.
There are two properties to be mindful of in play and it’s entirely photosynthetic. Terrestrial plants use more nitrates vs ammonia than aquatic plants due to the availability of greater photosynthetic energy. They evolved with leaves under the sun, and in turn, enjoy more light energy which allows them to directly process nitrates more efficiently. Aquatic plants first absorb ammonia and will attempt to expend more energy if need be photosynthetically to consume nitrates so long as enough light energy is present.
The latter is more efficacious when the lighting is stronger which is not optimal for most aquatic plants nor the fish as the efficacy of nitrate consumption is quite related to the amount of light the plants are exposed to. Naturally submerged plants would see diminished light and evolve accordingly. But terrestrial plants evolved for this environment.
I used pothos and monstera in my tanks as well as Lucky Bamboo in a 3rd tank. A single, $20 pothos plant has virtually eliminated nitrates in the 120 and the same with the 125 since rehoming the pacu’s:
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The big (literally and numerically) surprise was the dracaena or Lucky Bamboo. The pothos reveled its full potential in under 2 weeks. Lucky Bamboo took longer to display results, about 4 weeks vs only 2 weeks for pothos, but the 'bamboo' in particular has reduced nitrates so greatly, I’m not confident I can measure
any at all with a liquid test kit now:
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In my disbelief, I went out and bought a fresh liquid test kit to see if mine had spoiled but again, NO nitrates! A fully stocked SA cichlid tank with 0 nitrates? It sounded crazy to me but of all of the plants I’ve tried, Lucky Bamboo is the nitrate eating champion thus far.
What the image does not show is their growth. In case you were wondering where all those nitrates went, the Lucky Bamboo has grown from 24" stalks to now 6' in height!
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One topic that will no doubt be raised and rightfully so, is the toxicity of certain plants and their utility in an aquarium. In particular, pothos is known to be toxic to some animals.
But in truth, nearly ALL Epipremnum/riparian plants, even monstera have this same toxin throughout the entire plants, leaves and roots. The toxin is Calcium Oxalate. It's not actually toxic to fish due to it's insolubility as it requires a very acidic environment to leach into the water as it becomes soluble at PH = 4.5. Above 4.5 it's remains crystalline which is the actual issue for dogs and cats as the crystals can cause irritation or sores in mammals.
But even if it contains any toxins, if your PH is above 4.5, it cannot leach into the water as it's insoluble.
Admittedly we performed no tests on this as the LFS owners have actually not seen an incident of toxicity with Epipremnum/riparian plants in any of their aquariums nor their customers. In truth, even if it were toxic, the leaching ability can only occur when the plant is cut AND the PH is below 4.5.
I don't bother with rooting cuttings. I just wash the roots and let them drape into the tank through the plastic lighting grid. Of all my fishes, only the Severums eat the roots (and the plecos eat the algae on the roots). I have seen my Severums eat the roots for years without incident:
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While it may not appeal to everyone, a single Epipremnum/riparian plant can remove virtually all the nitrates directly from the water column if given enough time (weeks). I wish this could be more extensive and exhaustive but given the limitations of our testing,
one thing I can say with confidence is there's no greater nitrate reduction one can get for a freshwater tank for $20!
