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Discussion Starter · #1 ·
Last week, I posted my latest article 'Potted Plants for Fish Breeding Tanks' (10 pages, lots of pictures) on my website. Article has new data since 2017 and resulted from a recent talk I gave to Raleigh Aquarium Society.

None of the tanks have any filters or water circulation. Most have just a scattering of STS (Safety-Sorb clay gravel) on the bottom. All plants are mobile--potted, floating, or semi-attached. Tanks are for breeding fish, so all plants can be easily pulled out to catch fish. Attached are pictures of one tank and a table of water parameters that I measured (on August 8, 2021) for the 10 tanks. Interestingly, nitrates were almost zero except for one tank with 10 ppm. This despite the usual heavy feeding and infrequent water changes. Also, you'll note I have gone back to keeping LED lights on for 13 hours/day to maximize plant growth. No siestas. No time for plants to rest!
 

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Discussion Starter · #14 ·
@dwalstad when you mention that you're keeping your lights on for 13 hours straight, without continuously running a traditional bubbling sponge filter or just a soft gentle current from a small powerhead or some combination of these things you're not too concerned about possibly suffocating levels of carbon for the animal life nor a deficiency for the plant life? I presume you recommend rather light stocking levels?

I'm trying to see the balance here is what i'm getting at. For years we've used a siesta period to build carbon back up for the remainder of the photoperiod and run our aerators at night to avoid an oxygen crisis for the sake of the animals. What's the practical advice here, given this new data and lack of powered circulation?
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?
The accelerated plant growth takes care of the algae. The siesta builds up CO2 --not enzymes--for submerged plants, which need it in water. Floating plants can get it from air. I consider their good growth essential. (See 'Aerial Advantage' chapter in my book.)

Don't have computer at this time, so my answers will be brief and delayed until I get new one setup.
 

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Discussion Starter · #16 ·
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?
You are an enthusiastic student!
I only stopped siesta because l wanted to look at my fish when l feed them at noon. I assume that it could make a difference for floating and emergent plants. Plants don't grow without light and these plants are not limited by CO2.
 

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Discussion Starter · #22 ·
Emergent plants grow faster than submerged plants. They can clean up the water of nutrients (e.g., nitrates, ammonia, toxic metals, etc) faster than submerged plants. But floating plants add no O2 to water. It all goes into air. In fact, their leaves block oxygen diffusion from air into the water, so they can actually decrease the O2 in an ecosystem. That's why you need to have BOTH submerged and emergent plants.

The pond folks know all about this. They always recommend oxygenating plants for ponds (e.g., submerged plants like Anacharis).

Another thing I would say is that my tanks (5,10, and 20 gal) are only 12 inches high. This shallowness helps with oxygenation as there is a large surface area compared to water depth. As tank depth increases, there will be less oxygen entering the system from the air. Oxygen will affect bacterial activity and that can change water purification and many other things.
 

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Discussion Starter · #26 ·
I was so encouraged by last month's measurements, that I monitored my ten tanks again yesterday. Note that I did not clean or change water in any tanks since the earlier measurements, except Tank # 1 (it got a thorough cleaning, plant pruning, and 50% water change).

The one tank without STS (#9) is definitely accumulating nitrates. Plants continue to do their job of removing nitrites and ammonia without filters, which is what I expected. But the removal of nitrates is totally new.
Font Parallel Pattern Number Symmetry
 

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Discussion Starter · #28 ·
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.
 

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Discussion Starter · #30 ·
Tank #9 was at 10 ppm nitrates a month ago. So it has gone from 10 to 30 ppm in one month. No water changes during this time.

I assume that plant growth and bacterial activity cannot keep up; nitrates will continue to accumulate. This tank is outside where temperatures are now getting cooler and there have been several rainy days without much light. That said, another tank (Tank #8) is outside and it shows low nitrates despite similar conditions. To make a definitive statement I would have to 3 tanks with STS and 3 tanks without, all in the house.

Nitrates alone are not toxic, but if I can, I prefer that they do not accumulate. I am thrilled with results for the other 9 tanks. In the past, my tanks with full substrates usually had 10-40 ppm nitrates.

Today, I cleaned out Tank #9 and did a 70% water change. I am so pleased that I may reset up this tank in the house with STS!
 

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Discussion Starter · #32 ·
Wow! Talk about confirmation!

I think that you have put two and two together. I agree that STS alone is a poor substrate and as a soil cover okay, but not the best. Oil Dri is in same category as STS--baked clay.

For the potted plant tank, though, STS and Oil Dri might be perfect! They have clay dust and porous crevices for bacterial attachment and colonization. Associated nitrifying bacteria, as they use oxygen, create the MILDLY anaerobic conditions for denitrification even in environments that don't seem anaerobic to us.

Others viewing my results have questioned whether the STS is taking up N directly. I don't think so. First nitrates are negatively charged, so they do not bind to soil particles. Second, plants prefer ammonia, so they aren't going to take up nitrates unless they absolutely have to. I know of no chemical reaction that would convert ammonia to nitrates. I believe what we are witness here is biological process.

Third, any ammonia binding to soil particles is a one-shot process. The NH4+ cation would have to compete with other cations for a limited number of negative binding sites on clay particles (my book, p. 126, Fig VIII-3). In contrast, nitrate respiration is a continuous on-going process. It never stops. Just as we use oxygen for our respiration, these bacteria are continuously drawing down on nitrates for their respiration.

I didn't think a scattering on the glass would make that much difference, but maybe it can.

I cleaned up and brought Tank #9 with 30 ppm nitrates inside where it will have lighting and temperature similar to a "Twin Tank," #7. My concern was that plants in #9 didn't have maximum growth because the lighting and temperature outside were not as favorable as indoors. Attached is picture of two tanks. I tried to make tanks as similar as possible-same water, lighting, fish load, etc. The only big difference is that there is no STS in #9. Starting nitrates for both tanks was zero on 9/12. Stay tuned!
 

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Discussion Starter · #33 ·
Preliminary results to report! I've measured no nitrates in Tanks #7 and #9 at 3 weeks. The nitrates that accumulated in Tank #9 while it was outdoors may have resulted from reduced plant growth due to lower temperatures (65F many days) and lower light levels than the indoor tanks. (I've taken PAR readings for shaded sunlight and it is MUCH less than overhead LED or CFL intensity.)

Still, the STS may have had an effect. My preliminary results don't really test it adequately.

Thus, I have ordered some pure KNO3 and NaNO3. What I can do is add enough of the KNO3 to each tank to produce 20 ppm nitrates in each tank. Then, I can monitor the two tanks to see if the STS actually makes any difference in nitrate levels.

Will nitrates go down faster in Tank #7? Will they go down at all? If results look interesting, I might repeat the comparison with NaNO3.

I ordered the two pure chemicals from HomeScience for a total cost of only $17.25. This will provide me with some cheap entertainment over the holidays!
 

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Discussion Starter · #35 ·
I don't think it matters here that much. Since I'm testing for the effect of STS, it could be that Tank #7 with the STS is the experimental tank and Tank #9 (without STS) is the control.

Here's some more food for thought:

Planned study with KNO3 additions is to figure out why my tanks don't accumulate nitrates. One possibility is that robust plant growth takes up the ammonia--preferred N source of aquatic plants-- faster than any nitrifying bacteria can convert it to nitrates. So I'm not sure that plants remove nitrates; they just prevent them from being generated in the first place. (In my tanks without filters, this is a possibility.) If I do see nitrate removal, it could be via denitrification. In that case, the STS layer in Tank #7 could make a difference, possibly by encouraging denitrification.
 

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Discussion Starter · #37 ·
Reporting unpredicted end of my STS experiment. Presence of STS bottom layer didn't seem to affect 10 ppm added nitrates. But within two days, 4 out of 36 guppies died in Tank #9 without the STS. Emergency! Measured 0.5 ppm ammonia in this tank. Thus, I abruptly ended the experiment by changing 75% of water and adding enough STS (6 cups) to cover bottom of Tank #9. My take: STS not only binds ammonium but provides attachment sites for bacteria that decrease ammonia levels. Thus, while plants purify the water, STS gives me an extra level of protection. Now, I have STS in all of my tanks. None have filters and last week I disconnected all bubbling from air pumps. Photo shows today's picture of Tanks #7 and #9 after stopping the experiment the day before. Water in #9 is a little cloudy due to clay particles, but that's fine. And if you use STS, please do not discriminate against clay cloudiness and rinse STS until the water runs clear. Clay has a HUGE surface area to bind ammonium and provide attachment sites for bacteria. Thus, I only rinse STS once before adding directly to the tank. Clay cloudiness is good!
 

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Discussion Starter · #39 ·
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.
 

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Discussion Starter · #41 ·
Just posted a revision of my Potted Plant article on my website.

In order to revise my Potted Plant Tank article, I tested the effect of an STS gravel layer on the potential removal of added nitrates. I added 10 ppm nitrates to a 20 gal tank with STS (Safe-T-Sorb) and 10 ppm nitrates to a matching 20 gal tank without STS. Goal was to see whether denitrification or nitrification explained the nitrate accumulation I had observed earlier in one of the 10 tanks described in my article. Over a period of 13 days, I measured absolutely no decrease in nitrates in either expt tank. Attached is file describing the expt testing STS's effect on the added nitrates.

Unexpectedly, I ran into a "lurking variable." The guppies in the expt tank without STS were from an older batch that I believe was genetically less "fit" than the batch in the expt tank with STS. Guppy fitness/age may have explained the deaths that occurred during expt, not absence of STS.
 

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Discussion Starter · #43 ·
Please read the article. The subject is complicated and has many variables and blind alleys. Dead fish may have been due to genetic weakness, certainly not nitrates. Nitrates are not toxic. (For a better experiment, I should have used randomly selected individuals in both tanks drawn from one guppy population.) STS is a minor variable that may be irrelevant. However, I believe STS or any baked clay type gravel may be useful, because of clay's known greater nutrient and bacterial binding capacity than sand or gravel or no substrate.

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."
 

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Discussion Starter · #49 ·
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.
 

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Discussion Starter · #54 ·
STS (Safe-T-Sorb) is a natural clay (montmorillonite of the smectite clay group) mined in western Tennessee (USA). The company's nearby plant heats the clay to 800 degrees F which produces a calcined clay (clay hardened via melting). That temperature results in a material that is partially ceramic. As such it is very absorbent and effective in soaking up liquids, which is its intended purpose. SEACHEM heats their clay from northern Georgia to a higher temperature (1,200 F) from which they get FLUORITE. (Reference: Neil Frank, noted planted tank expert.)

For making pottery, clay is fired/heated to 1,000 to 2,500F. The high temperature melts and hardens the clay particles, somewhat like heating sand to create glass. The clay becomes a ceramic, the hardness depending on the firing temperature.

Kitty litter is only heated to dehydrate (get rid of absorbed water). Dehydration can be done at much lower temperatures (250F? or 150C). Thus, kitty litter has no structure and rapidly breaks down into fine particles (i.e., mud). Mixed with an organic potting soil, kitty litter mud would be highly reactive--release aluminum to create aluminum toxicity?-- whereas any aluminum release from STS gravel would be much more gradual and controlled, such that plant roots could handle it.

Remember that clay is composed of aluminosilicate, meaning that all clays contain aluminum and have the potential to generate aluminum toxicity. In addition, tropical clays may contain iron oxides and aluminum oxides deposited inbetween clay particles. These oxide deposit can cause even more metal toxicity problems. In my book (p. 132) I describe a tank meltdown experience I had from mixing potting soil with just a little bit of laterite clay. It created iron toxicity.

Michael here describes mixing STS with soil. Another knowledgeable hobbyist reported getting good results potting plants in a mixture of STS and soil. STS has a good reputation from experienced hobbyists, including our very own Michael!
 

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Discussion Starter · #65 ·
My biggest concern in this thread is introducing toxicity to the tank. When I read the above past about clay contain aluminium or iron it just makes me thing I should stick to inert substrate. The plants might not grow as well but they grow and the fishes don't have to worry about long term poisoning.

I think the biggest question i have given the above comments on clay is how do you know if any of the products are safe for long term use. I realize this thread doesn't seem to focus on fish health but isn't that a concern when picking your substrates ?


In nature, fish are found in lakes with clay sediments and rivers filled with turbidity from clay particles. Neutral pH and oxygen in aquariums and most natural waters neutralize aluminum and iron toxicity. (Iron and aluminum oxides are not toxic to fish, plants, or humans.) Plant roots in anaerobic substrates are the vulnerable ones, not fish.
 

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Discussion Starter · #67 ·
I'm assuming the baking process affects a chemical change of some sort upon the iron.
Yes. High heat changes the chemical bonds so that the atoms no longer react. It does not change the atomic composition.
 

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Discussion Starter · #68 ·
Thank you for this explanation, Diana. I have page 132 permanently bookmarked in my copy of Ecology of the Planted Aquarium (EPA) and, for whatever reason, it is only clear to me now that you were writing about toxicity to plants, not fish.

If I revise book, I will try to make this more clear. It is certainly an important point, so thanks for bringing it to my attention!
 
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