About filtration

[Boris]

Big foam filter media will tend to do a fair amount of denitrification and still not result in water which is short on oxygen. I do not need to do all sorts of complicated testing to know this. I use these filters in tanks where I keep Hypancistrus species breeding and growing out. I have a lot of Xingu river fish and they live in water temps from the low 80s F to bouts of time at 90F+. This water temp tends to hold less oxygen than cooler water. But the fish have a need for high oxygen levels. My plecos do not die very often, do grow nicely and do reproduce successfully, QED the water must be OK in terms of oxygen levels being adequate and nitrogen levels being almost absent (i.e. not testable without expensive lab equipment).

Hello again!
I am slowly learning and getting to grips with the topic and at the moment I have three tanks recently set up with different approaches.

In the first sentence quoted above, do you mean nitrification instead of denitrification?

[TwoTankAmin]

No, I meant denitrification. There are a type of bacteria called facultative anaerobes (or aerobes). These are able to function using oxygen or, when oxygen is depleted, use an alternative. For some this is nitrate. When they use nitrate the end product is nitrogen gas which returns to the atmosphere.

Because there is such a massive volume in a mattenfilter for the bacteria to form the bio-films in which they live, over time a great variety of microorganisms will colonize the foam. The result is there will be some pathways through the foam where the aerobic organisms will use all of the oxygen in the water following that pathway through the media. What there will be instead is the nitrate produce by the Nitrospira (nitrite oxidizers). When this occurs the facultative bacteria will switch from using O to NO2. The result is this nitrate never makes it back into the water column, it is broken down.

Every nitrifying bio-film will have some small parts that do the same thing, even when not using massive media. However, in such cases the amount of denitrification in the average filter is not significant and we do not even know it is occurring as our nitrates will still build up.

[Boris]

Thanks!
That is what I was thinking.
My plans for a Synodontis tank were put on hold due to the recent restrictions on movement so in the meantime I got a group of C. moorii for the 100 gallon.
I also installed a matten filter but since the tank was up and running I didn't want to empty it to install a corner filter I opted for a full width version. This is 50x50 cm and I was afraid 2" would be too flimsy so I doubled up and have 4" of 10 ppi across one end.
I have seven medium size fish and feed what they will eat once a day. If it is frozen mysis it is 2 cubes, if that means anything.
My impression is that the nitrates are increasing much slower than I expected and, checking the numbers now when I write this, they seem to be slowing even more as time passes. At the end of last month I had 10 ppm, did a 50% water change. A few days later I measured 3 ppm and am now at 5 ppm.
I concluded that there must be some denitrification going on somewhere but that would mean water with 6 mg/l oxygen going in and somewhere within those 4" reaching 0,2 mg/l which sounds incredible but I haven't got a clue to how much ammonia can be converted with 1 mg oxygen.

[dw1305]

Hi all,

.......but I haven't got a clue to how much ammonia can be converted with 1 mg oxygen.

As molar values it is NH4+ + 2O2 and as mass its 1.00 NH4 + 3.56 O2.

I had 10 ppm, did a 50% water change. A few days later I measured 3 ppm and am now at 5 ppm.

I'm a bit wary of nitrate test kits. Because all nitrate compounds are soluble you have to reduce nitrate (NO3-) to nitrite (NO2-) before you can form an insoluble coloured compound. There also some issues with Ion Selective Electrodes, mainly interference from other monovalent anions.

cheers Darrel

[Boris]

mg/l is mass but what is ppm, is it mass, volume or molar?

Yes, I know you have cautioned about hobbyist test kits but they do give a trend which follows prediction. After a water change they show a steady increase until the next WC and when you start up a new tank you get the increase-decrease curves on NH, NO2 and NO3 so i think they are useful for the purpose?

[Bas Pels]

As ppm stands for parts per million, one would assume it refers to a molar - 1 micromol of something per mole of something else.

The reality is different, ppm is most often read, by aquarists, as mg per liter. A millionth of the mass

I got to admit, it is rather distracting, after all, a liter of water is 55.52 mol of water. Adding to that 135,5 mg of cupper (II) chloride, that is 1 millimole, would give 1/55,52 or 0,01801 ppm, particle based

But in mass, it is 65 mg of cupper ions in 1 liter. Thus 65 mg/l or 65 ppm mass based

Personally, graduated in chemistry, I never use ppm, as it is quite confusing.

[TwoTankAmin]

I was pretty much taught what Darrel said about nitrate testing. I was also taught that the nitrate kit is most inaccurate in the 0 - 20 ppm range.

Think about how many routes water can take through a matten set-up. Then consider the fact that the bio-film does not form uniformly inside all that foam. The result is in one place there is lots of O left in some of the water exiting the matten and in another place it follows a pathway where the O gets used up before it can exit. Because the facultative bacteria can switch between oxygen and nitrate, where inside the foam denitrification occurs can change.

I was also taught that one of the things that occurs inside a matten is it will deal with a lot of the waste that has the potential to cloud the water and/or to break down into ammonia. Some of the organisms inside the matten consume organic waste before it can become ammonia which needs to be handled via a different process. This, of course, does not result in nitrate.

it is one thing to talk about the world of microorganisms, it is another actually to wrap one's mind around a totally invisible universe of these things inside our tanks. However, "the proof is in the pudding." When we see our water is always clear and nitrate etc. appears to be lower and the fish are healthy and even spawning and the offspring are thriving, something good must be happening.

[Boris]

This thread has links to threads with links so I am not sure where I read it but somewhere, I think it was Darrel, mentioned "offgassing through a plenum"?
There are no results when I search this forum for either plenum nor Novak but are you familiar with Dr. Kevin Novak?
He advocates having a plenum (gap) between the substrate and the bottom glass. The aim is to eliminate anaerobic areas and to avoid the sulfate reducing bacteria.
It can also promote the facultative anaerobes and denitrification to nitrogen gas which I think was meant in the quote above?
I have used the under gravel filter I had to create such a plenum under 2" of fine sand in the 100 G.The lift tube from the UGF is led through the matten filter so the slight low pressure created by the MF works toward a very slow downward movement through the sand.

What are your thoughts on this?

[dw1305]

Hi all,

There are no results when I search this forum for either plenum nor Novak but are you familiar with Dr. Kevin Novak? What are your thoughts on this?

I am, my thoughts are that he doesn't understand why his "UKAPS: biocenosis buckets are successful, or how they work.". Unfortunately he has removed a lot of the posts, picture and videos from his blog. I was interested in talking to him, but he was less interested in talking to me.

.....I think about how many routes water can take through a matten set-up. Then consider the fact that the bio-film does not form uniformly inside all that foam. The result is in one place there is lots of O2 left in some of the water exiting the matten and in another place it follows a pathway where the O2 gets used up before it can exit. Because the facultative bacteria can switch between oxygen and nitrate, where inside the foam denitrification occurs can change.........
it is one thing to talk about the world of microorganisms, it is another actually to wrap one's mind around a totally invisible universe of these things inside our tanks. However, "the proof is in the pudding." When we see our water is always clear and nitrate etc. appears to be lower and the fish are healthy and even spawning and the offspring are thriving, something good must be happening.

My guess is that is what is happening.

It is worth listening to Stephan Tanner, who is <"linked in earlier in the thread">.

Also have a look at <"Deep gravel....."> (also linked in earlier). It is quite a long thread but it will repay reading.

cheers Darrel

[Boris]

I was pretty much taught what Darrel said about nitrate testing. I was also taught that the nitrate kit is most inaccurate in the 0 - 20 ppm range.

I was also taught that one of the things that occurs inside a matten is it will deal with a lot of the waste that has the potential to cloud the water and/or to break down into ammonia. Some of the organisms inside the matten consume organic waste before it can become ammonia which needs to be handled via a different process. This, of course, does not result in nitrate.

However, "the proof is in the pudding." When we see our water is always clear and nitrate etc. appears to be lower and the fish are healthy and even spawning and the offspring are thriving, something good must be happening.

I am going through the "deep gravel" thread and there is so much information to digest and also some points I would like to clarify but we will have to take them bit by bit so as not to be confused.

@TwoTankAmin I am not calling you out specifically by quoting your post. It just had the right context.

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...
Despite the inherent uncertainty they seem to work for what we use them for.

We are taught many things but have you also experienced them to be true?
I am experiencing an apparent lack of nitrates associated with my matten filter so now I can start calling it knowledge? I find that, especially with filtration, there is often very little real data behind various statements.

Something good must be happening and that is fine for this tank but in order to replicate it on future tanks I need to know exactly what is going on?

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?

[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.