Nitrogen Removal in a Planted Tank

[CACAdmin]

Here's an intersting article by Diana Walstad about nitrogen in a planted tank: Nitrogen Removal in the Planted Aquarium (http://www.bilyap.com.tr/magazin/mag3/concept1S3.php)

What I particularly found interesting is her discussion of the soil underlayer in a tank.


She states: "My aquariums not only have plants, but they have a soil underlayer. This soil underlayer would be expected to contain huge numbers of bacteria, many more than in the overlying water or in gravel substrates. This is because soil has an enormous surface area for bacteria. Also, the soil layer would be anaerobic, providing perfect conditions for denitrifying bacteria to use (and remove) nitrates.
In my 70g heavily planted tank, I have a soil underlayer which has occurred naturally though the breakdown of food, waste and plant matter as I only gravel vac areas which don't have plants. The ability of the denitrifying bacteria in the soil could explain why this tank is the most stable one I have and has minimal nitrates at all times (even when heavily stocked).

Definitely an interesting read, and food for thought.

[OldMan]

Jay, I found the concept intriguing enough that one of my tanks is set up with potting soil rather than garden soil and it is well on its way to being my favorite planted tank. I did cap the potting soil with a coarse sand to keep the stuff from floating around.

[CACAdmin]

I think that effectively creates a similar situation as to my course gravel and the decaying matter sinking beneath it, although your more closely adheres to what Diana Walstad created in her tanks.

Just remember, don't do what I did when re-aquacaping and pull up the plants:rolleyes: ... it pulls up all that soil too which becomes suspended and must be fitered out (thus filtering out so much of the bacteria which resides in it). Snip the roots of plants you want to relocate in a circle around the plant (leaving about an inch of roots extending from the stem as I gather this is sufficient to sustain the plant) The roots left in the soil decay and add to the existing soil.

[Rain]

I have a 10 gallon all set up with potting soil capped with flourite just waiting for plants. I am glad to hear others have had success with this method. I'm really interested to see how it works for me.

I had thought about using sand to cap the soil but I was worried about the sand compacting. I've never used sand before so I don't have any experience with it. I do like the look of it though, and would like to try it.

[OldMan]

My sand is fairly coarse Rain, some people would call it a fine gravel. It is heavy enough to hold down the real substrate while being coarse enough to allow water to penetrate easily and avoid stagnant layers outside the potting soil. The potting soil is expected to become stagnant and provide the right environment for the plants and anaerobic nitrogen consumers to feed the plants the nitrogen through the root zone. It is one of the factors leading Diana to say that water changes are not needed more often than every 6 months.

[Melody]

This is all very interesting. It should be doable with pots too, yes?

[OldMan]

I have never tried the approach with a pot Mel but I don't see why it couldn't work. The pot itself would become the anaerobic region if it had a potting soil in it. If you are doing an El Natural, you do need the fast growing plants to consume lots of your nitrogen and the floating plants to prevent algae build up and to minimize the need for CO2. Floating plants like duckweed can get their CO2 from the atmosphere.
There is a bit more to it than just the potting soil if you want everything to work out, but it is fairly simple to care for once it is set up.

[Melody]

I'm kind of stealing one aspect for the specific benefits it brings as opposed to doing a natural tank, which I should have specified, sorry about that. It should do what it does for a natural tank I assume, but I wonder if the soil & topper would be too deep in a pot? I don't want any compacting issues, and I'm not sure if there's a depth limit before that becomes a problem... I really have to stop trying to do this plant stuff halfas...er...willy nilly :wink:, and do some thorough research . Thanks for the info - it's a really interesting concept all around.

I have a natural tank for all intents & purposes, by the way. It's just a little 5g and it started when I never got around to replacing a filter...lol. I put all of my miscellaneous plant bits in it, all floating. It only has a couple of fish in it along with Red Ramshorns and I feed very sparingly. I keep it more for the plants as they grow well in there without the water depth interfering with light penetration, plus it gets some natural light as it's beside my patio doors (no direct sun). The plants grow and pretty much fill the tank, which I thin out occasionally. I dose fert's about 6 times/year at best :rolleyes: . It's been there for a couple of years or so and does very well.

[OldMan]

If you follow Diana's way of thinking, you dose ferts every time you feed your fish. The concept in her approach is that the mineral content of a well balanced fish food has everything the plants need except things like calcium. By feeding the fish "generously" you feed the plants and the fish. The water you need to add for evaporation takes care of minerals like calcium. I would suggest you read up on her approach since it sounds like you lean that way anyway.

[Rain]

I'm actually giving it a try with pots too. I've put a couple pots with plants it them in my 20 gallon grow out tank for my guppies. It is otherwise a bare bottom tank. The pots have 1 inch of potting soil and 1 inch of flourite (I can't seem to find a fine gravel around here in a colour I like so I ended up using some black flourite I have). One pot is acutally a tupperware container, the other a small terracotta pot. We'll see how it works.

I've seen other people put plants in pots and then bury the pots most of the way into the regular gravel substrate. I guess that way you could give one plant a more nutritious substrate without converting your entire tank.

[Edgezilla]

plants root expell O2 during photosynthesis. If there are roots in the soil, than it is not an anaerobic environment. The huge surface area of the soil is good for bacteria that helps the plant uptake nutrients.

Thats what make ADA soil and similar product great because they are very porous and easy for the roots to grow into compare to gravel which is not porous. Before all the fancy claybase substrate, Flourite was a good choice because it is more porous than gravel. I still use them in my smaller tank for the sake of cleaniness.

My emersed setup has little to no algae and the concentrated nutrient solution is exposed to 2x 54watt HOT5. The only difference is I use hydroton so there is a lot of O2 to help the plant uptake the nutrients and tonnes of surface area for good bacteria to grow on. For comparison, I keep the PO4 at 10 ppm in my emersed setup which is way more than a normal 1-2 ppm in the aquarium.

I had an emersed setup outdoor for Echinodorus 4 years ago with NO3 in the upwards of 40 ppm exposed to direct sunlight with no algae.. Just tonnes of calcium slime build up.

[BlueAbyss]

plants root expell O2 during photosynthesis. If there are roots in the soil, than it is not an anaerobic environment. The huge surface area of the soil is good for bacteria that helps the plant uptake nutrients.

This is true to an extent... at least with emerse plants with submerged roots (http://books.google.ca/books?id=TEy-_q9s7OYC&pg=PA165&lpg=PA165&dq=plant+roots+O2&source=bl&ots=DZWF93fUFM&sig=h83sCDdElhxyYQ5LiPYz2hT0cpk&hl=en&ei=ku35Se34PIqeMvLgzbgE&sa=X&oi=book_result&ct=result&resnum=3), though the roots are relatively gas-tight in order to keep the oxygen inside the roots and reduce the amount that diffuses out into the soil area. The plants attempt to keep the oxygen in the root zone for themselves, though the area immediately surrounding the roots (probably within a half inch of a major root) will probably be relatively oxygen rich. Beyond that, or if the plants are quite slow growing and don't produce that much oxygen during the photoperiod, the substrate is likely to be anoxic (anaerobic).

This would provide for a very diverse mix of bacterial fauna of both aerobic and anaerobic types, which would explain the excellent plant growth (lots of bioavailable nutrients and minerals as far as plants are concerned) and the low nutrient levels (most would be taken up or bound as soon as they were available). A similar situation can exist in reef aquaria, where people are getting strong algae growth but with no detectable nitrates or phosphates... they are getting taken up as soon as they are available, so they test as 0 even though they are actually still there or being leached from somewhere.

[Edgezilla]

If anerobic theory holds true in aquarium, than why is it that ADA soil and similar substrate with very porous structure / massive amount of surface area create more problems when left uncheck? I had quite a few anerobic spot caused by wood placement in the tank; where lights don't shine and plants don't grow. For about a year when I didn't feed the plants, the roots were no longer than 3" per plant. so there was tonnes of anerobic spot.

I have not had a substrate more finiky than ADA soil in all these years I have kept a planted tank. The substrate is so porous, all the nutrients leeched back into the water column so fast that I get greenwater within a matter of day if I forget to feed the plant. Of course, I can do what most people do and blindy use EI method and just dump everything in excess quantity and hope that it works out for the best. But I don't want to have 30 ppm of NO3 and 10 ppm of PO4 by the end of the week just so the tank is free of algae. I keep sensitive plants that can't tolerate high salt level. feed enough to grow the plants, not overfeed and count on a miracle.

The idea is very similar with soil.. It has a very porous structure so water can move freely in there. Don't add a capping of gravel to the soil and I can tell that all people will see is algae bloom or cloudy water from the garden soil. soil absorb the nutrients like a sponge and release it back into the water after.

Most of the time, the excess nutrients in the water is used by algae. That is why algae infested tank usually detect little to no excess nutrients because the algae is using up the nutrients which create more algae. All we can do is use algae as a guide to determine what nutrients is in excess of. When more inhabitant is added to the tank, more nutrients of different type is increased as well. You can't add one thing without increasing another. Add soil with nutrients, better have plants consume the nutrients or algae will take over. Add soil as a nutrient sponge, better hope your plants can grow fast enough or expect nutrients to be release back into the water.

My secret to growing plants is not following any of the PPS, EI or PMDD or rely on anerobic environment to control the nutrients. I base my dosing on seeing what algae is in the tank and add accordingly so I am not over dosing and putting the inhabitant at risk and wasting fertilizer and CO2.

No one aquarium is the same and we can't go blindly follow the general consensus and expect good results or efficiency. How many inhabitants are in the tank? How thick of a substrate layer do they have? What kind of substrate do they use? what kind of plants do they have?


Different plants uses different kind of nutrients at different level. If Terrestial has so many different type of formula why do we follow the typical 10-1-8 N-P-K guideline? Is it because its easy to use and don't need a degree to grow plants? I don't see people growing terrestrial plants having a degree. All the people with degrees did the breakdown for the general public so they can easily access fertilizer with preset formula for lawn, bulbs, evergreen, waterplant, and etc.

I was following EI for the a while and added 1/4 tsp of PO4, 3/4 tsp of KNO3 to my 75g every 2nd day and I still had algae. I used PPS but it couldn't keep up with the beefheart feeding in the tank. I tried not dosing and plants died because the excess nutrients from beef heart, fishwaste, and etc were not of the type the plants need.

As for anerobic environment, when I pulled out my cryptocoryne scurilis, it had 18" long roots running at the bottom of the tank.. and this plant was in area where the substrate is 2.5" deep.

On average, there is 2.5" of substrate for roots to grow, a heavily planted tank consist of a larger varitey or stems, rhizome, rosette, foreground is bound to have the roots all tangle up forming a network of roots below the substrate. So theres usually not a lot of anerobic spot in a well established tank.