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Thank you for posting this. I read it as soon as I saw it referenced in one of the community threads and knew immediately that it deserved a thread of its own (but didn't want to get in front of you to do it.)

What can I say? What lovely tanks! What a lovely variety of sizes and shapes of jars and pots! IMHO, this is the future of the Walstad method because so many people have established tanks that have been cycled for years, who want to take the hobby to another level of naturalness but don't want to completely tear up their tanks in order to do so.

I also love how you have incorporated many of the issues discussed on these pages into one article, making the information even more accessible to the general public.
 

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Biggest surprises:
1) That DW herself has only been filterless since 2019. This "confession" makes me feel as though we are all learning new things together (or, in "real time" as the kids like to say.)
and,
2) Her hypothesis that beneficial bacteria in the gravel (specifically, in Safe-T-Sorb, a kind of baked clay with industrial applications) could be a source of nitrate uptake. This is huge. It goes against years of indoctrination that nitrification is a one-way street.
 

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From what I have been able to glean from dozens of posts on this subject, the two main points of a siesta schedule for lighting purposes, are that 1) a completely submerged aquatic plant pretty much uses up its ability to to uptake CO2 within the first four hours of daylight. That's because of the loss of a certain enzyme crucial in the photosynthesis process. The enzyme builds back up during the siesta period. So, it's not really as if you are gaining any more oxygen by leaving the lights on for 13 hours straight. The main benefit of the siesta period is

2) that it mitigates the growth of algae. Maybe, DW is less worried about algae in a potted aquarium?
 

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My shipment of Safe T Sorb just arrived. There are no trucking supply stores near me in Brooklyn and the cheapest online supplier was about triple the deal they gave DW. That being said, and even with delivery costs - it was still in line with other gravel advertised for aquarium use but at about 10x the quantity!


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I will probably not need this much gravel for the next 50 years, but I was really anxious to test out DW's theory about nitrate eating bacteria. If true, it would be a game changer for hobbyists who have already cycled their tanks and cannot stuff their tanks with enough fast growing plants to outcompete bacteria for ammonia and ammonium.

Safe T Sorb is a really interesting substrate in its own right. Coarser than potting soil but nor quite as chunky as ordinary gravel.
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I was tempted (and still am) to take out all my pots and just lay down a thin layer on top of the mulm filled bottom of my porcelain bowl. But instead, I'm going to stick a container of it in a corner of the bowl and see what sort of parameters I get after a week or two. I rinsed out about two cups full and was pleased that, despite some bad reviews it received in another internet community ten years ago, it rinsed fairly easily and without a lot of residue.

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Well, two cups turned out to equal about four inches of Safe T Sorb in my old cannister compartment and despite the fact that it contained no organic material, it seems granular enough that ways to mitigate the possibilities for it becoming anaerobic still seemed advisable. So I mixed about a dozen bio-filter media in with it. And, I sat it on top of another cannister compartment that would remain empty.
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Again, counter some advanced warnings, there was surprisingly little buoyancy when I placed the whole thing into my bowl (I did use the compartment cover to submerge it - but, took it off as soon as the contents were completely under water.)
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Thanks, @dwalstad! I think you've given us a homework assignment until your new work station is set up. I've already started re-reading Ch. IX of EPA. :giggle:

EDIT: Yes, and there's also the piece in Ch.VI ("Carbon") that sums it up nicely:
To compete, submerged plants have had to invest in costly photosynthetic equipment (enzymes) to capture CO2 when it is available. When CO2 is depleted, though, such as in the afternoon during intense photosynthesis, this equipment lies idle [skip] Plants must still maintain underused or idle equipment; this maintenance drains energy from the plant in the form of increased respiration. The result is reduced photosynthetic efficiency - and ultimately growth - of the freshwater plant. (p.94)

So, yes. I either misread this the first time I sped through it or missed it entirely. The presence (critical mass) or absence of CO2 in the water is clearly the precipitating factor where submerged plants are concerned.

But, this still begs the question, why cease the siesta periods in your potted plant tanks? Is it because so many of them are potted emergent plants?
 

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They take CO2 straight from the air. Underwater, plants have a harder time getting CO2. It's so important, they (aquatic plants) change their leaves so it'll be easier to get CO2.
Does that mean that with aerial leaves aquatic plants can produce more O2? If so, where does all that extra O2 go and does any of it wind up in the water column?
 

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Well, I know it's only been 5 days but I wasn't going to have another chance to measure my parameters for a while. Nevertheless, with only one or two top offs for the past month, my ammonia is still 0 ppm, nitrites 0 ppm and nitrates somewhere between 5 and 10 ppm. Five days ago, the nitrates stood somewhere between 10 and 20 ppm. Normal variation between test samples? Maybe. Put it this way, my parameters rarely improve without a partial water change and I haven't performed one in three weeks. I culled the floaters at the same time that I installed the Safe T Sorb, so it could be either one of them - or both acting in concert. Will check again in about a week.
 

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Well, I know it's only been 5 days but I wasn't going to have another chance to measure my parameters for a while. Nevertheless, with only one or two top offs for the past month, my ammonia is still 0 ppm, nitrites 0 ppm and nitrates somewhere between 5 and 10 ppm. Five days ago, the nitrates stood somewhere between 10 and 20 ppm. Normal variation between test samples? Maybe. Put it this way, my parameters rarely improve without a partial water change and I haven't performed one in three weeks. I culled the floaters at the same time that I installed the Safe T Sorb, so it could be either one of them - or both acting in concert. Will check again in about a week.
So...it's been a week and I gotta say...I'm impressed. I just tested my parameters again: 0 ammonia/ammonium, 0 nitrites and this time there's no question, the nitrate level is firmly parked at 5ppm. That's nearly two weeks during which my nitrates have not increased and, to the contrary, have trended in the opposite direction. I have even attempted to "control" for the growth of my floaters:
Plant Houseplant Fluid Terrestrial plant Aquatic plant


As you can see, the salvinia minima is corralled behind plastic tubing and has had little room for growth the entire week, normally a recipe for rising nitrates in my bowl. My hypothesis, now a theory, is that denitrifying bacteria have taken up residence in my bowl and the most likely location are the unique surface crags and crevices presented by the STS introduced at the beginning of my observations.
 

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It's also the Mother Nature club. :)

I value your input, because it has some thought (e.g., grasp of denitrification) AND you have read my book.

I am very excited about the nitrate results. I have long suspected that in a tank without CO2 injection, plants alone couldn't take up all the nitrogen.
THANK YOU. And, while I have you...About that #9 tank of yours. Is that a stable 30ppms or do you periodically have to change the water? Just curious.

EDIT: Same question, but phrased slightly differently. Number 9 tank went from 10 ppm nitrates to 30 ppm nitrates in a month's time. Are the plants in that tank able to keep it within that range by themselves or do you have to intervene before things reach a dangerous level?
 

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I guess this is one of those "the proof is in the pudding" moments:
Liquid Fluid Wood Paint Floor


Now, if that's not 0 nitrates, I don't know what is!
This has been a very interesting last couple of hours because in attempting to answer another question on the "Suitable soils for the Walstad tank" thread, I wound up doing a deep dive on STS only to discover that the stuff has been around for ages. People have always been attracted to its natural, river bed color - and the fact that it is dirt cheap (no pun intended.) It's amusing to read from the benefit of 20/20 hindsight that everyone's initial desire was to use it as a straight substrate. I think because it looked so natural like soil that they had to be disabused of the notion that it contains any nutrients at all. People also wanted to use it as a cap only to discover that it was lighter and airier than gravel and held plants down only with difficulty.

Only one post mentioned STS in connection with the denitrification process and that was only because of its resemblance to Oil Dri, another tractor supply substance that was being touted as the main medium in a so-called, "anoxic filtration system". But, that's a subject for another thread. What's remarkable here is that STS seems to be creating the conditions for anaerobic bacteria to thrive without actually being anaerobic, at least not in ways that are familiar to any of us on APC.
EDIT: familiar to us who work with dirted tanks.
EDIT: Perhaps, it's not a biological process at all, but a chemical one?
 

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This is a wonderful venture on your part, sure to be of interest no matter the results. One technical question, since it's been a while since I've taken a science course: Technically speaking, which tank would be considered the "control"? The one w/o or the one with the STS?
 

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So, what was going on with the spike in ammonia? Does something similar to DAP (p.66 EPA) occur? In that section, you described a reaction whereby certain bacteria convert nitrates into ammonium. I suppose one could imagine a situation where there is an excess of nitrates that triggers a similar reaction that results in higher ammonia?
 

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It would be impossible to sort out all the variables to make a definitive statement. I doubt the ammonia spike was due to DAP, because DAP is associated with fermentation and very anaerobic sediments.

Time will tell on this one. My goal is to continue to raise and breed guppies in these potted tanks without filters, pumps, and mechanical aeration. Tanks will depend on plant growth with STS as a backup.
It was a noble effort. Each one of your guppies deserves a posthumous medal!
 

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Ah, but did the expt tank without STS register a spike in ammonia as happened in your previous nitrate dosage? That was the baffling part (IMO). it was almost as if something was reverse engineering the extra nitrate back into ammonia?

Wait. I guess I should read the article first. :giggle:

EDIT: Never mind. DeadFish= increase in NO3.

Fascinating. So, we're still left with the puzzle of STS somehow increasing nitrification without - seemingly - to increase nitrates. Possible explanations being that plants are perfectly capable of increasing their uptake of nitrates? Potted plants?
 

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The main take-home message is that good plant growth in 9 out of my 10 tanks removed toxic forms of nitrogen- ammonia and nitrite. I now believe--based on my experiment--that the nitrate accumulation in the outdoor tank was due to nitrification, not denitrification Overall, the article trumpets "Plant Power."
Oops. I just realized i should have said "DeadFish=increase in NH3"
Be that as it may,
i still applaud you for the effort. It's made STS a tad less mysterious and reinforced the primacy of biological processes that are already familiar to hobbyists. For me the take-home message was: every tank is different.
 

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I'm sorry but what is STS ? I really can't keep track of all these abbreviations.
STS= Safe-T-Sorb

To quote from an earlier post:
People have always been attracted to its natural, river bed color - and the fact that it is dirt cheap (no pun intended.) It's amusing to read from the benefit of 20/20 hindsight that everyone's initial desire was to use it as a straight substrate. I think because it looked so natural like soil that they had to be disabused of the notion that it contains any nutrients at all. People also wanted to use it as a cap only to discover that it was lighter and airier than gravel and held plants down only with difficulty.

Only one post mentioned STS in connection with the denitrification process and that was only because of its resemblance to Oil Dri, another tractor supply substance that was being touted as the main medium in a so-called, "anoxic filtration system". But, that's a subject for another thread. What's remarkable here is that STS seems to be creating the conditions for anaerobic bacteria to thrive without actually being anaerobic, at least not in ways that are familiar to any of us who work with dirted tanks.
Some of us theorized that STS might have been initiating some sort of ionization process in the water like some of the commercially available products already on the market, but @dwalstad eliminated that as a possibility fairly early in her speculations.
 

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STS, because of its porosity and clay component and high surface area, has plenty of binding sites for nutrients (CEC or 'cation exchange capacity'). It also has plenty of attachment sites for bacteria. If the STS is anaerobic, say at bottom of a deep substrate filled with organic matter, it will support denitrification, an anaerobic process. On the other hand, if the same STS is in an aerobic environment with enough oxygen, it will support aerobic bacteria like nitrifying bacteria. It simply provides attachment sites for bacteria, and since it also binds nutrients (NH4+, K+, etc), it encourages bacterial activity.

Apparently, the thin layer of STS scattered on the bottom of my potted plant tanks stays aerobic, and thus, does not support denitrification. I wasn't sure about this until I did my experiment showing that 10 ppm added nitrates did not decrease over a 13 day period. If tanks were actively denitrifying, I should have measured some decrease in nitrates.

I bought a 40 lb bag of STS for $7 at Tractor Supply Co.
So, it's still conceivable that someone (not saying who necessarily) could concoct the right anaerobic conditions for denitrifying bacteria to thrive by say, stacking a couple of old filter containers filled with STS on top of each other and just letting them sit at the bottom of their tank?
Plant Flowerpot Compost Annual plant Soil
 
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