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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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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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Thank you for the article. Really interesting, especially since I just started a new tank couple of months ago with potted plants.

I'm interested how the 13 hour light period affected the tank in overall? Since I've been using the 5 hour - 4 hour siesta - 5 hour cycle.
 

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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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@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?
 

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@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?
Maybe I'm misunderstanding, but wouldn't running the lights for 13 hours straight add more oxygen to the water? Since the plants are photosynthesizing the entire time? As opposed to the siesta time, when they start consuming oxygen again.
 

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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.
@dwalstad just wanted to add my thanks for this article. Such a great resource to have on hand, lots of really concise information. I love my full-substrate Walstad, but now I'm really itching to set up a tank with potted plants!!
 

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Maybe I'm misunderstanding, but wouldn't running the lights for 13 hours straight add more oxygen to the water? Since the plants are photosynthesizing the entire time? As opposed to the siesta time, when they start consuming oxygen again.
That's what I'm trying to wrap my mind around. I guess what I'm asking in my own confused way is
1. Are we relying solely on other processes like decomposition and animal respiration for the carbon during lights on and
2. What happens at night when there is no photosynthesis but neither is the water being disturbed to dissolve more O2? This is more an animal welfare question.

I'm also thinking the answer here is also dependent on stocking levels. Apologies if I wasn't clear. Such is the hazard of trying to follow up on your hobby and work from home at the same time o_O.
 

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I have a small 5G filterless tank filled with crypts and endler-guppy hybrids. The tank definitely keeps the livestock in balance, in number and smaller size of the fish.
 

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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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Algae, I must admit, is a perennial concern of mine that the siesta period pretty much eliminated along with lots of healthy plant growth and not fertilizing the water column. I tell you, it's hard changing things up when you get used to doing things a certain way. I've always had at minimum a sponge filter with a powerhead and an airstone that comes on at night. They're almost protective charms for me at this point. Not very scientific, but there you are.
 

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I have a high tech tank in which all plants are mobile, either epiphytes on rock or potted. There is a thin layer of gravel barely cover up the bottom to eliminate reflection. I do it so I can easily move plants around to rescape without the mess of having to break up rooted plants in substrate. I use hydroponic net pots that allow roots to reach out and stay aerobic, and small rock for epiphytes so I can take them out to repot or re glue with no hassle.

In my zero tech shrimp bowl with no water movement, plant mass is the sole source of oxygenation as surface gas exchange is mostly blocked by floaters. The bowl receives afternoon window sunlight and I can see O2 bubbling up like a fountain. Water testing showed that nitrate and phosphate are nearly non detectable at all time despite light feeding and regular partial water change with nutrient rich water from my high tech tank.
 

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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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@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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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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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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I measured CO2 throughout the day on an NPT tank. The CO2 dropped a bit but there was still plenty of CO2. I think it was 15ppm down to 13ppm but rose up when the lights are off.
But, would that not be the case when/if most of your plants are lucky bamboo, papyrus palms, and lotuses?
 

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But, would that not be the case when/if most of your plants are lucky bamboo, papyrus palms, and lotuses?
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.
 

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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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