About filtration

[TwoTankAmin]

I came to all this by a strange route. About a dozen or so years back, maybe more, I got curious about things I would see an almost any fish site. One of those was that the nitrifying bacteria in tanks die off at the rate of 10% a day w/o any ammonia. Another was one must always do massive water changes when you test an see ammonia at .25 or .50 or higher. I set out to see if I could find some science on the subject. And that led me to Google Scholar and a lot of scientific papers/articles/books.

I read a ton and even had a few email conversations with the authors. One of them was Dr. Tanner of Swiss Tropicals. He is why I have Mattenfilters and Poret foam cubes instead of the typical tanks sponge filters.

I am familiar with a lot of the basics of all this stuff but I am far from being a trained scientist. However, I am also observant. Somewhere on this site I have posted a picture of one of my tanks with a Mattenfilter. Somebody, commented on how clear the water was. This was when I first realized this fact. I am wired to notice just the reverse. I don''t need to know when a tank is going well, I need not to miss when something is going wrong

I must confess my initial motivation to migrate towards Mattens and Poret cubes was the result of the fact that they required cleaning much less frequently than other forms of filtration and media I was using. I am now in my early 70s and wanted to be doing less work each year without suffering any loss in water quality. I got the less work but had to settle for even cleaner water.

One last thing re nitrate tests. What I meant was not that the reading would fluctuate but that they would be inaccurate. By that I mean that given the process involved, the small sample size, how easy it is to be slightly different on drop sizes and in then in shaking the reagents, errors would be greatest in the range of 0 and 20 ppm. How much does it matter to most if they have an 80 ppm reading which is really 5 ppm higher or lower? It matters a lot more at lower concentrations. Where I think the kit is most useful is to see changes up or down. The only time I even test for nitrate is when doing a dry season where I am doing fewer water changes, I want rising TDS but not from rising nitrate.

[Boris]

I came to all this by a strange route.

So what was your conclusion and why the poret foam?

Pothos seems to be considered one of the best immersed plants for nitrate uptake.
I have had pothos in my big tank for a few years. At first it grew great but it eventually stopped growing but still looked healthy. I thought that it may be a lack of light but never got round to getting a grow lamp for it.
When I got the moorii they started eating at the roots. I put them in a submerged breeding box but had to cut the end to get the curled stem to an acceptable position. I waited a couple of weeks but no roots developed so I moved it to another tank with around 10 ppm nitrate for two weeks and it started growing some roots. I then moved it back to the big tank but the roots are not growing. Instead it is consuming old leaves, one by one. I think it is simply starved of nutrients due to the denitrification in the MF?
I have read somewhere that pothos doesn't grow well below 20 ppm?
Isn't new growth the only nutrient sink? If it simply "lives" it is not using much nitrates?

[dw1305]

Hi all,

I have to disagree on the nitrate tests. There is very seldom an "off" measurement or random fluctuations. If you take a measurement every other day you don't get: 3 5 10 5 15 10.. but rather a consistent 3 3 5 5 10 10 15...

Try diluting your tank water samples down, and see if that still holds true. It isn't that NO3 values are always wrong, they just have a certain amount of uncertainty about them.

I find that, especially with filtration, there is often very little real data behind various statements.

You would need to go and look at the scientific literature on waste water treatment, aquaculture and phytoremediation.

Regarding the plenum, I have divided nitrification and denitrification between the MF and the substrate. If I have well oxygenated water, do you see this as functional or does it have an inherent problem? One point could be that the substrate can not be siphoned so all waste must be processed in tank increasing BOD?

I don't mind where nitrification (and potentially) denitrification occurs. The only exception is for denitrification in a canister filter, which is a recipe for disaster.

cheers Darrel

[Boris]

Try diluting your tank water samples down, and see if that still holds true. It isn't that NO3 values are always wrong, they just have a certain amount of uncertainty about them.

EDITED: If you mean measuring low concentrations then yes, I do get the same result? The biggest source of inaccuracy is that I am subjectively comparing the sample to a chart of different shades of yellow.

You would need to go and look at the scientific literature on waste water treatment, aquaculture and phytoremediation.

I mean in common aquaristics. I have not seen any data to back up the claims of what various filters and filter media have in terms of properties or capacity.
I see large sumps with several compartments, each with a different type of media. One has filter foam in sheets or cubes. The next is a fluidized bed of K1. Next has bags of ceramic rings and then bags of lava rock etc. It seems to simply be hedging your bets because you don't know which one actually works and "you can never have too much filtration"!
The ceramic rings that you got with canisters and was said to have "enormous surface area" has been replaced by the more large pored sintered glass varieties (perhaps they realized that too fine pores don't work well?) but filters like the FX6 still comes with mostly foam preinstalled. Perhaps that is a clue?

I don't mind where nitrification (and potentially) denitrification occurs. The only exception is for denitrification in a canister filter, which is a recipe for disaster.

I agree but I am asking for your opinion or "SWAG" about the plenum idea?
Also, what is a suitable flow rate through a canister filter?
If you have four baskets of media and the oxygen is depleted within the first two then the remaining two will be anoxic?

On Novak's anoxic filter, I get your point about the plants in the photo but I understand that some people have had success with it in ponds or tanks without plants so it may still work?
Reading "Mankysanke's" explanation it seems reasonable but for one thing and that is that the negative charge of the clay particles constantly draws the positive ammonia toward the center. Why doesn't the ammonia stick to the first negative ion exchange surface it hits?
If I am right and "Mankysanke" is wrong then it would work almost as well with filter foam instead of clay?
http://www.mankysanke.co.uk/html/anoxic_filtration.html

[Lycosid]

Reading "Mankysanke's" explanation it seems reasonable but for one thing and that is that the negative charge of the clay particles constantly draws the positive ammonia toward the center. Why doesn't the ammonia stick to the first negative ion exchange surface it hits?
If I am right and "Mankysanke" is wrong then it would work almost as well with filter foam instead of clay?
http://www.mankysanke.co.uk/html/anoxic_filtration.html

It seems like Mankysanke is claiming that the center is more negative (and, obviously, the outside is full of positive ions) which causes the ammonia to "switch partners" constantly, moving inwards each time. This sort of behavior is possible for ionic bonds, which are not bonds between two specific atoms (normally) but between an atom and all of its oppositely-charged neighbors. Covalent bonds would require a full-blown chemical reaction to dissociate every time.

I have no idea if he's right, but this isn't an impossible thing.

[Boris]

It seems like Mankysanke is claiming that the center is more negative (and, obviously, the outside is full of positive ions) which causes the ammonia to "switch partners" constantly, moving inwards each time. This sort of behavior is possible for ionic bonds, which are not bonds between two specific atoms (normally) but between an atom and all of its oppositely-charged neighbors. Covalent bonds would require a full-blown chemical reaction to dissociate every time.

I have no idea if he's right, but this isn't an impossible thing.

So the best way to test this would be to make it as a reactor, feed it ammonia and see what happens?

[Boris]

Somewhere on this site I have posted a picture of one of my tanks with a Mattenfilter. Somebody, commented on how clear the water was. This was when I first realized this fact.

Now that you say it I have also noticed that there is very little suspended particles in my tank also. When I installed the plenum/under gravel filter I anticipated a lot of waste on, and in the sand but no, not much on the surface and very fine particles stirred up from the sand. Not enough to warrant a water change!

[dw1305]

Hi all,

.........I mean in common aquaristics. I have not seen any data to back up the claims of what various filters and filter media have in terms of properties or capacity.
I see large sumps with several compartments, each with a different type of media. One has filter foam in sheets or cubes. The next is a fluidized bed of K1. Next has bags of ceramic rings and then bags of lava rock etc. It seems to simply be hedging your bets because you don't know which one actually works and "you can never have too much filtration"! The ceramic rings that you got with canisters and was said to have "enormous surface area" has been replaced by the more large pored sintered glass varieties (perhaps they realized that too fine pores don't work well?) but filters like the FX6 still comes with mostly foam preinstalled.

A lot of the claims made by companies that manufacture "premium biofiltration media" are just smoke and mirrors, and would be picked apart by any scientist in seconds.There are values for Kaldnes type floating cell media, because they were developed for salmon aquaculture and have been widely used in the wastewater industry, they are designed to shed biofilm if it becomes to deep.

It isn't the media that is important it is the dissolved oxygen, microbial nitrification is very rarely limited by lack of physical media, it is limited by the amount of dissolved oxygen.

..... about the plenum idea?

I don't see any advantage to a plenum, but I only keep planted tanks where plant root growth is going to provide the zones of fluctuating REDOX in the rhizosphere.

Also, what is a suitable flow rate through a canister filter? If you have four baskets of media and the oxygen is depleted within the first two then the remaining two will be anoxic?

That is the issue, so flow through the filter needs to be fast enough so that the water is still oxygenated when it leaves contact with the filter media. A canister filter is different from a HOB, HMF or Trickle filter, it is a sealed vessel and the only oxygen entering it is in the water.

Why would you want to attempt anaerobic denitrification in the filter, when you run the risk that ammonia and nitrite can build up in the aquarium water? If your filter is a "nitrate factory" it just shows that nitrification is effective. Worrying about nitrate is like being more concerned about the splinter in your finger and ignoring the fact that your arm is hanging off.

On Novak's anoxic filter, I get your point about the plants in the photo but I understand that some people have had success with it in ponds or tanks without plants so it may still work? Reading "Mankysanke's" explanation it seems reasonable but for one thing and that is that the negative charge of the clay particles constantly draws the positive ammonia toward the center. Why doesn't the ammonia stick to the first negative ion exchange surface it hits? If I am right and "Mankysanke" is wrong then it would work almost as well with filter foam instead of clay? http://www.mankysanke.co.uk/html/anoxic_filtration.html

Anaerobic denitrification can work, it is used a lot in wastewater treatment, usually with a temporal or spatial separation between the processes. Plant/microbe biofiltration is potentially a lot more effective, but you need a bigger footprint for your treatment facility and you may have climatic issues in temperate zones.

In terms of the clay, you are looking at Cation Exchange Capacity, which is dependent upon both valency of the ion and its abundance in the water column, so it would be fair to say I'm dubious, because all multivalent ions are more strongly bound.

Affinity series: Cations: Al3+ > H+ > Ca2+ > Mg2+ > K+= NH4+ > Na+

cheers Darrel

[Boris]

A lot of the claims made by companies that manufacture "premium biofiltration media" are just smoke and mirrors, and would be picked apart by any scientist in seconds.

It isn't the media that is important it is the dissolved oxygen, microbial nitrification is very rarely limited by lack of physical media, it is limited by the amount of dissolved oxygen.

That is the issue, so flow through the filter needs to be fast enough so that the water is still oxygenated when it leaves contact with the filter media. A canister filter is different from a HOB, HMF or Trickle filter, it is a sealed vessel and the only oxygen entering it is in the water.

This is exactly my point!
95%(?) of hobby fish keepers, fish store staff etc, even very experienced people, have a poor understanding of the whole "filtration" process and have no desire to try. The advertisement statements made by manufacturers not only go unchallenged but become truths spread and defended within the fish community. Once you start questioning it it quickly falls apart and you have to deal with a bit of confirmation bias on what you have been told and taught for so long.
This is the first place I have found scientifically literate people who are willing to explain these topics without getting emotional.
Thank you all!

[bekateen]

This is the first place I have found scientifically literate people who are willing to explain these topics without getting emotional.
Thank you all!

That's why I like this site. I get so much good information and support.

Cheers, Eric

[dw1305]

Hi all,

This is exactly my point!
95%(?) of hobby fish keepers, fish store staff etc, even very experienced people, have a poor understanding of the whole "filtration" process and have no desire to try. The advertisement statements made by manufacturers not only go unchallenged but become truths spread and defended within the fish community. Once you start questioning it it quickly falls apart and you have to deal with a bit of confirmation bias on what you have been told and taught for so long.

This is the first place I have found scientifically literate people who are willing to explain these topics without getting emotional.
Thank you all!

I'd whole-heartedly agree with that, my experience is that certain companies are really keen to send you a "legal letter" if you write about their products in anything less than complementary terms, but won't supply any scientific data whatsoever, and hide behind proprietary information, trade secrets etc.

Have a look at <"UKAPS: Bedside Aquarium"> & <"So what is organic waste">.

cheers Darrel

[Lycosid]

It seems like Mankysanke is claiming that the center is more negative (and, obviously, the outside is full of positive ions) which causes the ammonia to "switch partners" constantly, moving inwards each time. This sort of behavior is possible for ionic bonds, which are not bonds between two specific atoms (normally) but between an atom and all of its oppositely-charged neighbors. Covalent bonds would require a full-blown chemical reaction to dissociate every time.

I have no idea if he's right, but this isn't an impossible thing.

So the best way to test this would be to make it as a reactor, feed it ammonia and see what happens?

Well, if you specifically want to test the idea about the negatively-charged clay you should make two reactors, one with clay and one with something else as close as possible in all characteristics except electrical charge. One real possibility here is that things work, but not the way the creator thinks they do, and that some of the tweaks to enhance performance don't work because they are based on an incorrect theoretical understanding of how the device works.

Overall, if you are looking for nitrate removal the way that I think is easiest and least likely to accidentally poison everything is to use fast-growing plants in the aquarium that you trim back (assuming that you remove the plant trimmings from the aquarium).

[dw1305]

Hi all,

......Overall, if you are looking for nitrate removal the way that I think is easiest and least likely to accidentally poison everything is to use fast-growing plants in the aquarium that you trim back (assuming that you remove the plant trimmings from the aquarium).

That would definitely be my take home message as well.

cheers Darrel

[Boris]

Hi all,

......Overall, if you are looking for nitrate removal the way that I think is easiest and least likely to accidentally poison everything is to use fast-growing plants in the aquarium that you trim back (assuming that you remove the plant trimmings from the aquarium).

That would definitely be my take home message as well.

I am not so much trying to solve a problem as exploring possibilities.

Do you have any thoughts or experience on my problem with pothos not growing?
About plants bringing oxygen down into the substrate through the roots, this article by Diane Walstad says that aquatic plants prefer ammonia to nitrate even in root uptake. Nitrification close to the roots would seem to be a disadvantage for the plant unless there is an even bigger advantage in some other aspect?

https://dianawalstad.files.wordpress.co ... n2017a.pdf

[Bas Pels]

I followed the lead but the main reference is to a book / which I would have to buy. Not the best way to convince me.

Aparet from that, she wrote that people, even if they have a planted tank, misunderstand the amount of nitrogen taken up by plants.

I must say - it is rather easy to estimate this amount, as all nitrogen taken up is used for producing proteins. in fact, the whole schedule, ignoring al details, is

proteins from fishfood -> excreted ammonia -> proteins in plants

Now our fishfood contains 30 to 50 % of proteins, and the plants around 5.

That is, only if you take out around six to ten times the weight of plants a week than you´ve fed, will the plants keep nitrates at bay.

Almost all my tanks are planted, but I estimate I only take out at most the same weight as I feed in the best of them.

[dw1305]

Hi all,

.... she wrote that people, even if they have a planted tank, misunderstand the amount of nitrogen taken up by plants.

proteins from fishfood -> excreted ammonia -> proteins in plants

Now our fishfood contains 30 to 50 % of proteins, and the plants around 5.

That is, only if you take out around six to ten times the weight of plants a week than you've fed, will the plants keep nitrates at bay.

I understand where you are coming from, but that makes some assumptions that aren't necessarily right.

You have the muscle growth of the fish to take into account, and also that plants create a much larger area where nitrification (and denitrification) may occur in the substrate, in the zones of fluctuating REDOX in the rhizosphere.

The 5% figure, for the protein content of plants, includes those that have a lot of structural carbohydrates ("fibre"), true aquatic plants don't, so their protein content is typically much higher.

This was one of the reasons why I originally used Duckweed (Lemna minor) for the "Duckweed Index".

From <" Duckweed - a potential high-protein feed resource for domestic animals and fish">

......The concentration of nutrients in dry matter of a wild colony of duckweed growing on nutrient-poor water typically is 15 to 25% protein and 15 to 30% fibre.

Duckweed grown under ideal conditions and harvested regularly will have (in dry matter) a fibre content of 5 to 15%, a crude protein content of 35 to 43%, and a polyunsaturated fat content of about 5%......

That also highlights two of the other advantages of floating plants,

• They aren't CO2 limited, so can potentially take up a lot more fixed nitrogen should it become suddenly available, and

• They form a negative feedback loop where increased nutrient availability cause increased nutrient uptake

The plant with the greatest capacity for fixed nitrogen uptake is probably Water Hyacinth (Eichornia crassipes), but plants like Salvinia auriculata group and Pistia stratiotes show a similar response.

cheers Darrel

[dw1305]

Hi all,

Do you have any thoughts or experience on my problem with pothos not growing?

No, it grows in some of the tanks in the lab. in pretty much RO water. Might be a light issue?

About plants bringing oxygen down into the substrate through the roots, this article by Diane Walstad says that aquatic plants prefer ammonia to nitrate even in root uptake. Nitrification close to the roots would seem to be a disadvantage for the plant unless there is an even bigger advantage in some other aspect?

It takes less energy for the plant to uptake NH4+ ions, but they are capable of using all forms of fixed nitrogen (NH4+/NO2- and NO3-).

In natural systems fixed nitrogen is a very limited resource, so plants grab any they can, in any form. As analogy you might prefer bank notes to coins, but they are all cash.

cheers Darrel

[Boris]

About plants bringing oxygen down into the substrate through the roots, this article by Diane Walstad says that aquatic plants prefer ammonia to nitrate even in root uptake. Nitrification close to the roots would seem to be a disadvantage for the plant unless there is an even bigger advantage in some other aspect?

It takes less energy for the plant to uptake NH4+ ions, but they are capable of using all forms of fixed nitrogen (NH4+/NO2- and NO3-).

In natural systems fixed nitrogen is a very limited resource, so plants grab any they can, in any form. As analogy you might prefer bank notes to coins, but they are all cash.

cheers Darrel

Yes, I understand that but if the plant didn't release oxygen from the roots, the same ammonia that reached this zone would not be nitrified and could be taken up by the plant at less cost. The plant is "giving" the bacteria the oxygen that it then has to reduce again.

[Boris]

I followed the lead but the main reference is to a book / which I would have to buy. Not the best way to convince me.

Aparet from that, she wrote that people, even if they have a planted tank, misunderstand the amount of nitrogen taken up by plants.

I must say - it is rather easy to estimate this amount, as all nitrogen taken up is used for producing proteins. in fact, the whole schedule, ignoring al details, is

proteins from fishfood -> excreted ammonia -> proteins in plants

Now our fishfood contains 30 to 50 % of proteins, and the plants around 5.

That is, only if you take out around six to ten times the weight of plants a week than you´ve fed, will the plants keep nitrates at bay.

Almost all my tanks are planted, but I estimate I only take out at most the same weight as I feed in the best of them.

I can't seem to find that part.
Are you referring to the article about plants preferring ammonia to nitrate?

Edited to add:

I now have two tanks where denitrification is almost omitting the need for water changes to remove excess nitrates. If I add plants they only need to pick up the difference.
I have Walstads book on its way in the mail but I have not read it.
However I have suspicions that she is attributing too much to the plants and too little to microbes.

[TwoTankAmin]

Here is a paper on the transport of oxygen to the roots and then releasing it in an anaerobic zone and this dramatically changes what if happening in the substrate and how it benefits the plant. I have posted this before.

Petersen, Nils Risgaard‐, Jensen, Kim, (1997), Nitrification and denitrification in the rhizosphere of the aquatic macrophyte Lobelia dortmanna L., Limnology and Oceanography, 42, doi: 10.4319/lo.1997.42.3.052
https://aslopubs.onlinelibrary.wiley.co ... .42.3.0529

It is an older paper but it is still a good indication of what can occur in a planted substrate.

[dw1305]

Hi all,

Yes, I understand that but if the plant didn't release oxygen from the roots, the same ammonia that reached this zone would not be nitrified and could be taken up by the plant at less cost. The plant is "giving" the bacteria the oxygen that it then has to reduce again.

It is really all down to amounts, any available ammonia is going to be taken up by nitrifying micro-organisms and plants and it is never going to accumulate and will always be below 1 ppm. It is different for nitrate, it isn't as energy rich, so can build up to ~30 ppm even in natural situations.

cheers Darrel

[dw1305]

Hi all,

I have Walstads book on its way in the mail but I have not read it. However I have suspicions that she is attributing too much to the plants and too little to microbes.

No I don't think she is. It is always plant/microbe nitrification when you have plants, and since she wrote her book there has been a lot of scientific work that has shown that plant/microbe biofiltration can potentially deal with much larger bioloads (an order of magnitude larger) than "microbe only" filtration. (From th linked paper "Myriophyllum aquaticum Constructed Wetland Effectively Removes Nitrogen in Swine Wastewater")

In this study, a three-stage surface flow CW was constructed in a pilot-scale within monospecies stands of Myriophyllum aquaticum to treat swine wastewater. Steady-state conditions were achieved throughout the 600-day operating period, and a high (98.3%) average ammonia removal efficiency under a N loading rate of 9 kg ha-1 d-1 was observed. To determine whether this high efficiency was associated with the performance of active microbes, the abundance, structure, and interactions of microbial community were compared in the unvegetated and vegetated samples. Real-time quantitative polymerase chain reactions showed the abundances of nitrifying genes (archaeal and bacterial amoA) and denitrifying genes (nirS, nirK, and nosZ) were increased significantly by M. aquaticum in the sediments, and the strongest effects were observed for the archaeal amoA (218-fold) and nirS genes (4620-fold). High-throughput sequencing of microbial 16S rRNA gene amplicons showed that M. aquaticum greatly changed the microbial community, and ammonium oxidizers (Nitrosospira and Nitrososphaera), nitrite-oxidizing bacteria (Nitrospira), and abundant denitrifiers including Rhodoplanes, Bradyrhizobium, and Hyphomicrobium, were enriched significantly in the sediments.

To get around the uncertainty of what goes where researchers have used the differing isotopes of nitrogen to try and find out where fixed nitrogen ends up.

I'm not sure which papers everyone has access to, but "<Plant diversity increases N removal in constructed wetlands when multiple rather than single N processes are considered">says

(3) isotope fractionation in the rhizosphere of Coix lacryma‐jobi was primarily due to microbial denitrification while multistep isotope fractionation was detected for Phragmites australis and Acorus calamus (indicating recycling of N), suggesting that species differed in the way they transformed N; (4) the enhanced N removal at high diversity may be due to mutualistic interactions among species belonging to different functional types. Our findings demonstrated that although plant species richness had negligible effects on individual N‐cycling processes, it enhanced the overall ecosystem functioning (N removal) when these processes were considered collectively.

cheers Darrel

[Lycosid]

I have Walstads book on its way in the mail but I have not read it.
However I have suspicions that she is attributing too much to the plants and too little to microbes.

I have Walstad's book. I thought it was very good.

Disclaimer: I also know Diane Walstad (although not well).
Disclaimer to the disclaimer: this means I also know that she raises a lot of fish (especially fancy guppies, these days) and takes her own advice, sometimes running experiments to verify ideas. So while she could be mistaken about why something works she's promoting ideas that she has made work, and my impression is that she is generally careful and cautious.

[dw1305]

Hi all,

I have Walstad's book. I thought it was very good......... I also know that she raises a lot of fish (especially fancy guppies, these days) and takes her own advice, sometimes running experiments to verify ideas. So while she could be mistaken about why something works she's promoting ideas that she has made work, and my impression is that she is generally careful and cautious.

I think the passage of time has made it even more impressive as a book.

No-one else has attempted to write anything of similar scope, and, while you might not agree with absolutely everything in it, 99% of it is veritable gold-dust.

It is the book I wish I'd written.

I really admire both Diana Walstad and Tim Hovanec for having embraced scientific change and revised their opinion based on more recent research (either their own, or by other scientists).

I started posting about "cycling" based on our findings from working on the phytoremediation of waste-water. It was before I knew about all the novel nitrifyng micro-organisms, but I was pretty sure the linear view of cycling wasn't right.

cheers Darrel

[dw1305]

Hi all,

..........I have posted this before.

Petersen, Nils Risgaard‐, Jensen, Kim, (1997), Nitrification and denitrification in the rhizosphere of the aquatic macrophyte Lobelia dortmanna L., Limnology and Oceanography, 42, doi: 10.4319/lo.1997.42.3.052
https://aslopubs.onlinelibrary.wiley.co ... .42.3.0529

It is an older paper but it is still a good indication of what can occur in a planted substrate.

There is an updated paper on the effects of Lobelia dortmanna on rhizosphere microbial assemblages:
"The effect of Lobelia dortmanna L. on the structure and bacterial activity of the rhizosphere". K Lewicka-Rataj, A Świątecki, D Górniak - Aquatic botany, 2018

I have access if any-one wants a copy? But the key findings were:

• The significant influence of L. dortmanna on microbiological processes in the sediments was confirmed. Clearly the high amount, biomass and metabolic and physiological activity of bacteria in the rhizosphere sediments confirmed the stimulating effect of isoetids on sediment bacteria.

• High redox potential and high bacterial respiration rate in the rhizosphere.

• High DOC concentration results in high bacterial activity in rhizosphere.

• CO2 concentration in rhizosphere depends on the number of active bacteria cells.

cheers Darrel

[Boris]

Thank you all three for the links and info!

I am not claiming to contradict Walstad or anyone else. I am simply going through the process where I learn something, think about it, have an idea and then learn why my idea was not correct.

While waiting for Walstad's book to arrive I have done another experiment:

In a 12 gallon I covered the bottom with 1/2" of soil from my dads garden compost. On top of that at least 2" of sand. I used a 50/50 mix of sand/gravel and made a gradient so there is 1 1/2" at front and 3" at the back.
Small sponge filter, two air stones.
No plants! Add water and measure nitrogen.
Expectation:


I don't know how to display a table here.
Result:
Day: 1 3 5 7 8
NH: 0.2, 0.4, 0, -, 0, 0
NO2: 0.5, 0.4, 0.5, 0.1, -, 0
NO3: 5, 5, 10, -, 0,...1,...

Day nine I added 10 small tetras. Day 17 I added another 20 tetras.
Six weeks in nitrate is constant at 1ppm.

So in 8 days I had not only ammonia and nitrite but also nitrate go to zero.
I assume that the necessary amounts of bacteria were present in the soil as a sort of "instant cycle"?

One caveat is I later learned that the "soil" is actually 100% leaf detritus.

[aquaholic]

I am not going to get into the filtration discussion but if you wish to have a low maintenance tank, apart from low stocking rate, I would utilise automatic water change. If you add an overflow, you can apply slow continous drip 24/7 to diplace tank water out. Adding new water in drips allows you to use low pressure piping (very cheap) and your drainage line could be as small as airline tube. If you are adding 3% or less of tank volume daily, you do not need to worry about removing chlorine or chloramine. You do not need to be cleaning filters. You do not need to worry about temperature fluctuations in winter. The auto water change will reduce your maintenance routine, save time and increase safety margin for livestock whether you have one tank or several hundred tanks.

[Boris]

if you wish to have a low maintenance tank, apart from low stocking rate, I would utilise automatic water change.

Yes, automatic water change is a future plan and apart from reducing maintenance it adds stability which may be an underrated quality in our fish keeping?
The only(?) drawback of this is that it is still a wasteful way. The past years have had reoccurring limits to water sources and consequently water usage around the world and even where I live. Reducing the volume of water needed may become increasingly important.

However a certain amount of water change may be necessary for other reasons than nitrogen.
What other reasons are there for small, but reoccurring water changes?

[Bas Pels]

Apart from nitrogen, it looks like fish, at least some species, produce pheromones, reducing the ability of conspecifics to grow.

From my own experience, a single fish in a tank will grow, whether I change water or not. If there are more in the tank, growth will reduce if I don't change water, even if the amount of fish is the same (thus the amount of non-conspecifics is less in case of more conspecifics)

I did not read about it, anywhere, but there does seem to be something

[TwoTankAmin]

Your tap water contains a number of things. Some might evaporate, some may get taken into the fish, some get used by plants. Your fish produce waste that is not merely ammonia. Over time things that are needed get used up. Carbonates are a good example. Things that are not used up because they are not needed can build up and that may cause harm. Other things will get depleted. So think of water changes as restoring the balance to the water.

Every system is different. In my case weekly large water changes work well because we have our own well, so that is what I do. For others a drip/overflow systems works best. There are many ways to deal with water changes and multiple ways to drain and refill. But the goals is always the same, remove the unwanted and replace the used up.