Plant filtration and Nitrates

[Cohazard]

I'm planning to build an overhead sump/refugium type setup on my heavy stocked goldfish tank, not just because goldfish are fat waste producing beasts, but also because my tap has high nitrates.

My goal is to reduce nitrates to 0-10ppm on a consistent basis.


I'm looking for people who have experience with testing their nitrates before and after beginning plant filtration to suck up nitrates, so i can get an idea of how many plants i'll need to accommodate to make an impact.

Thanks in advance!

 

[JK47]

Nitrates straight out of the tap sucks. Sorry to hear that. I can tell you with relative certainty that plants won't lower you much (noticeable) below where you nitrate level is out of the tap. Plants consume ammonia first prior to consuming nitrates. Plant filtration essentially reduces the nitrate levels by avoiding the nitrification process to some or a large extent.

Once yours plants adjust to the main (consistent/abundant) food source that would mostly be ammonia, the nitrate from the tap will be last to be consumed. Dependant upon your stocking levels the plants may never get to that stage. If that makes any sense

 

[Cohazard]

That makes sense, so it sounds like I'll be doing some testing on my own.

See what the plants can do with no ammonia (no fish, just the nitrates from tap) and compare that baseline to plants running on the main tank.

 

[Jez1992]

Have you considered a nitrate reduction vessel. We have them in the UK, so your tap water passes through it during a water change and removes the nitrate. However its not for using in the filter, more as a way of treating the water before adding to the tank. I'll post a link

 

[Jez1992]

What you want is the purolite selective nitrate resin:

http://www.devotedly-discus.co.uk/acatalog/Resin.html

 

[convict360]

I daresay pothos or devil's ivy would have a good impact

 

[Drstrangelove]

I'm looking for people who have experience with testing their nitrates before and after beginning plant filtration to suck up nitrates, so i can get an idea of how many plants i'll need to accommodate to make an impact.

Thanks in advance!

F1 Vet and I had looked at this in his pothos thread. In that thread he measured and tested his nitrates and we derived some anecdotal observations. (It was a a very uncontrolled experiment.) My examinations won't definitively answer your question, but it should help explain why your question doesn't have a simple answer.

Many plants have a definite effect on nitrate levels. However the effect is complex and dependent upon many variables that you won't necessarily be able (or want to take time) to control.

1) aquatic and terrestrial plants differ in their preference for nitrogen based molecules (ammonia, nitrates or nitrites are all nitrogen based.) (Eg., corn, roses and pothos are terrestrial, while most submerged plants are aquatic. They do not each consume each of the nitrogen materials at the same rate, sometimes having distinct preferences for one or the other.)

2) the amount of nitrogen-based absorption is likely directly related to the absolute mass growth of the total plant since nitrogen is a building block for many plants. A plant that adds 100 grams of mass will likely consume more nitrogen than one that adds 50 grams of mass.

However, plant growth rate is dependent upon many factors independent of the available nitrogen such as genetics, other nutrients, temperature, available light, etc. Adding light for example, which might increase total mass growth, will likely indirectly increase nitrogen absorption, assuming all other required nutrients are present, but nonetheless fast growing plants under low light might out perform slow growing plants under optimal light due to genetics.

3) plants differ in their ability or propensity to off-gas nitrogen. Off gassing (afaik) is basically a plant's ability to release nitrogen into the atmosphere under certain conditions. Off gassing may play a large role in how much nitrogen based molecules are removed from an area that is independent of the growth of the plant.

4) it's worthwhile (IMO) to consider plants as reservoirs of nitrogen. If the reservoir is full or damaged, it stops absorbing and may even begin releasing it's contents. Thus, removing or trimming back slow growing or damaged plants is part of the process to ensure that the plant is not releasing a large amount of nitrogen back into the tank.

Pothos and many aquatic plants are regularly used by people to reduce nitrate levels. They are probably not used as efficiently as possible (as you can see from above) because doing so is complex and demanding, but inefficient usage still seems to work effectively. If you take into account some of the factors listed above you can probably increase your efficiency and reduce how many actual plants you need.

 

[duanes]

I have used overhead sumps, and experienced first hand the ratio of plant mass to nitrate production Drstranglove spoke of, in my testing. Although pothos works well and I suspend it directly in tanks, I found a large semi-emergent plant such as papyrus, that required regular trimming took nitrate down much more quickly. Papyrus will grow 4 ft tall or more depending on sun, and availability of light. If placed in a sun drenched window, will use much more nutrients such as nitrate, better than a northern, less sunny exposure.
My nitrate testing produced 2-5 ppm readings when the papyrus was in maximum growth, @ 5 ppm in winter. But even with the plants, I still would do 30% water changes every other day on those tanks.

I also experimented with water hyacinth ending in poor results, because the hyacinth needed direct full sun, and UV that the inside windows seemed to block.

Pothos

Pothos roots growing down in a 2 ft depth tank.

 

[Coryloach]

I've been using emersed plants for years...Trust me, they wipe out any nitrogen pretty fast. Whenever I measured nitrates in the below type tanks, I barely got a reading...Instead I constantly battle plant nitrogen deficiencies and I actually dose additional nitrates in the form of dry fertilizers...

As for plants preferring ammonia, even better....The nitrification process itself alters the water chemistry in the tank, which in turn is harmful to the fish if water changes are not up to scratch...Nitrates on their own are not harmful, but high nitrates are a sign of tons of chemical processes fouling the water...The less available ammonia for nitrogen cycle, the better the water quality and that's the essential part of keeping plants. Another extremely good benefit is the ability of plants to reduce metal toxicity.

Emersed plants have an advantage of unlimited CO2, hence they are better at consuming nitrogen compounds.

Some examples of mine

And this one below is my new project, so not so many plants yet...See the yellow nitrogen deficient leaf on the peace lily to the right? Well, two generous feedings a day with 8 clown loaches, 9 denison barbs and 5 SAEs in this tank can't keep up with the nitrogen demand of the plants and they are just a few by my standards. All my plants in the tank are nitrogen deficient right now..I've increased my nitrate dose of KNO3 3 times to keep up......I've got floaters that are suffering with the same pretty badly...but on the mend now with additional dosing..Plants don't lie and react to lack of nitrogen and other deficiencies pretty fast....

You don't need testing. Your best test is emersed plants and floating plants given plenty of light...Old leaf yellowing/chlorosis is pretty much a sure sign of not enough nitrogen in the water for the plants. ..Nitrate tests on another hand are totally useless to tell you anything..Nitrogen in the form of nitrate is a mobile nutrient and affects old growth first but can affect new growth if plants are left severely deficient for a longer period.

 

[Coryloach]

By the way, the papirus on the picture duane posted above is severely nitrogen deficient, ha, ha...There goes your proof