Journal Marcel's next experimental design - suggestions welcomed

[Marcel G]

As some of you may know, I have done various experiments in the past. Among the most popular ones were:
(1) Nutrient consumption in planted tank
(2) Growth curve of 7 species of aquatic plants
(3) Analysis of aquarium substrates
(4) Plant preferences for water „density“

At the beginning of this year I returned to experimenting [after seven years]. Since then I have managed to conduct three experiments with the following plants so far: Ammannia crassicaulis, Ammannia pedicellata 'Gold', Bacopa salzmannii 'Purple', Cryptocoryne becketii, Limnophila aromatica, Limnophila hippuridoides, Pogostemon deccanensis, Rotala sp. 'Enie' and Rotala wallichii.

I am currently thinking about changing my present methods (recipes). The main goal is to find (= identify) a specific set of parameters that will ensure a good plant growth and can be easily replicated.

We all probably know that different plants have different requirements. I would therefore like to try to divide plants into certain "groups" according to key preferences, and then try to test this.

Here's an example:
There are plants that can only be grown in water (without any substrate). An example of such a plant is Rotala wallichii. To grow well, it needs absolutely no substrate, but it seems to require an acidic water, a relatively small amount of nutrients in water column and zero alkalinity (which is not to say that it would not thrive in other conditions ... but I have tested these conditions reliably for it). Then there are plants that [maybe?] need an organic substrate to grow well, others may possibly need a higher CO2 or higher bicarbonate levels (as carbon source) ... who knows. In this way, we could define a range of factors (parameters) that can play a key role in the successful cultivation of different groups of plants (which we sometimes give names such as undemanding, moderately demanding and very demanding).

So if you had eight test aquariums, what combinations of parameters would you use in each aquarium to test as many key factors as possible that might play the most important role in growing aquarium plants? In other words, try to suggest eight different recipes that could cover the basic requirements of most aquarium plants.

These are my eight recipes (combos), for example, which I think could cover the requirements of most plants:

1) organic substrate + recipe A (with bicarbonates) + extra CO2

Recipe A:
- cations = 20 ppm Ca, 6 Mg, 5 K, 5 Na
- anions = 24 SO4, 35 Cl, 22 HCO3
- all nitrogen (N), phosphorus (P) and microelements (Fe, Mn, B ...) are available to the plant in the substrate and therefore do not need to be in the water

2) identical to #1, but without extra CO2

3) organic substrate + recipe A (without bicarbonates) + extra CO2

Recipe B:
- cations = 20 ppm Ca, 6 Mg, 5 K, 2 Na
- anions = 24 SO4, 43 Cl, 0 HCO3
- all nitrogen (N), phosphorus (P) and microelements (Fe, Mn, B ...) are available to the plant in the substrate and therefore do not need to be in the water

4) identical to #3, but without extra CO2

5) no substrate + recipe C (with bicarbonates) + extra CO2

Recipe C:
- cations = 3 ppm NH4, 20 Ca, 6 Mg, 5 K, 5 Na
- anions = 10 NO3, 2 H2PO4, 24 SO4, 35 Cl, 22 HCO3

6) identical to #5, but without extra CO2

7) no substrate + recipe D (without bicarbonates) + extra CO2

Recipe D:
- cations = 3 ppm NH4, 20 Ca, 6 Mg, 5 K, 2 Na
- anions = 10 NO3, 2 H2PO4, 24 SO4, 43 Cl, 0 HCO3

8) identical to #7, but without extra CO2

Here is the same in table form:


PS: I intend to do all of the above recipes at room temperature (25°C = 77°F) and relatively strong lighting (~80-100 PAR at the bottom), as I believe they should be sufficient for most plants.

I will be grateful to anyone who comes up with their own reasonably substantiated recipe suggestion to test. I promise to take all comments into consideration when designing the next experiment. I will also be happy if you suggest plants suitable for testing in these recipes (please keep in mind that they must be commonly available plants).

 

[Tim Harrison]

Marcel, good to see you posting again in an open forum. This is a little over my head and I have little interest in the minutia of fertz dosing and water chemistry, so I can't really offer advice or opinion. But looks like a worthy experiment, and good to see applied science in action. I'll be along for the ride and the process, hope it works out. And also look forward to the results

 

[Burr740]

Hey Marcel, good to see you here

 

[GreggZ]

Marcel it's been a long time. Welcome and good to see you here.

As to your recipes all very interesting.

Which have you found to to work well with the widest range of plants? Many keep a large number of different plants these days and keeping them all happy at once seems to be the tricky part.

Setting nutrients aside, what would you say are other factors that contribute to a great planted tank?

 

[Marcel G]

This is a little over my head and I have little interest in the minutia of fertz dosing and water chemistry, so I can't really offer advice or opinion ...

I realize that too much detail will probably put a lot of people off, but I tried not to bother with too much detail (@PeerUnk can confirm that my original, unabridged methodology as I describe it on my site is a half-hour+ read), and I was kind of hoping to make it understandable. Anyway, no need to go into details. My point is more to "map the terrain" so to speak of the various relevant options. By "relevant" I mean those options that seem to you to be key. For example, I don't count temperature or flow among the key parameters, because I think we can all admit that at room temperature and decent water flow, most aquarium plants could probably grow well (so I consider these parameters as some kind of constants). So, in my preliminary design I use rather "non-limiting" amounts of nutrients (similar to Tom Barr) to eliminate the possibility that some plant species might be downright hindered from growing well by too small doses of nutrients. But it is quite possible that this may not be a correct assumption. Perhaps some plant species, on the other hand, require lower nutrient levels in the water column for good growth (e.g., plants from the Lythraceae family maybe). I would therefore be very glad if you could write your views on this, as you see it. Of course, the substrate must also be taken into account. If someone grows Ammannia successfully on a nutritious substrate with only a small amount of nutrients in the water, it is probably hard to conclude that Ammannia require low concentrations of nutrients, because they will have more than enough in the substrate ... etc. @plantnoobdude mentioned in another thread that he grows Ammannia pedicellata without problems even in inert substrate without "root feeding", but the question is how long he has had that substrate there and whether some detritus has accumulated over time, which would certainly bind some nutrients. That one uses extra CO2 though. CO2 can not only stimulate growth (if it is the limiting element), but also, as a result of the accelerated growth, the concentration of certain substances in the plant tissue can be "diluted", which can also lead to "detoxification". That is, if some plants were suffering from poisoning before the addition of CO2, the faster growth due to extra CO2 may cause a dilution of the toxic substance in their body, causing them to "recover". So this must also be taken into account. Also, @sudiorca is successfully growing Ammannia pedicellata 'Gold' (and even without CO2), but uses an organic substrate. Similar results have @PeerUnk, who grows Ammannia pedicellata 'Gold' in a regular vase (without CO2, in sunlight, with high nutrient concentrations in the water, but again on organic substrate). So what factors play a key role there? I'd say probably (1) the substrate, (2) water with its various parameters, (3) CO2, and maybe (4) bicarbonates and pH ... who knows. I don't know either. But I'd like to find out. My goal is not to find some one-size-fits-all recipe for all plants. I don't think that can exist by the very principle of differences between plants. But I would like to find some "basic set of recipes" that could cover the requirements of most aquarium plants and could be easily replicated. So, for example, if someone wanted to grow Rotala wallichii, they could use "Recipe #1" and be assured that it would grow nicely. If he wanted to grow, say, Limnophila aromatica, he could use "Recipe #2", etc. Of course, if he wanted to grow plants with significantly different requirements in the same aquarium, then he would have to find some compromise, but I don't want to go into that here. Sorry for the longer reply, but I just wanted to better explain what I was getting at.

 

[Marcel G]

As to your recipes ... which have you found to to work well with the widest range of plants? Many keep a large number of different plants these days and keeping them all happy at once seems to be the tricky part. Setting nutrients aside, what would you say are other factors that contribute to a great planted tank?

Hi @GreggZ, I think you can find the answers to most of your questions in my previous post (#5). As I wrote there, my goal is not to come up with a one-size-fits-all recipe, but rather a [easily replicable] set of recipes that can meet the requirements of most aquarium plants. For that reason, it is obvious that the recipes will certainly be different. The question is what exactly should they differ in ... what parameters are key for different groups of plants? As far as my results go, I don't have many yet. And most of them are rather a failure. Algae is the most common problem I struggle with. One of the few plants I can now grow systematically successfully is Rotala wallichii, which grows like a weed in my conditions (under moderate light and without extra CO2), but the appropriate recipe for it was not discovered by me, but by Maq (who got "banned" from ukaps.org, where he was still active some time ago). However, we have different views on goals and how to achieve them, so we no longer work together. Compared to him, my results so far are poor. Well, I'm learning not to give up, to take lessons even from failures, to get inspiration from various forums (even if their predictive value for me is not very high [due to superficially described parameters]) and to study scientific literature, and then to incorporate these findings into my practices. Anyway, don't let this overwhelm you in any way, because no matter what I do or how much I study, I am not immune to bias. I think even a garbage man (without any practical experience in our field) can come up with a properly reasoned opinion. While experience is certainly useful, we can often find the right path through simple logical reasoning.

 

[ElleDee]

What are your outcomes and how are you measuring them specifically?

How is the plant material being maintained before the experiment and how will you address the issue that plants often take time to adapt to new conditions, so initial growth in experimental conditions are not necessarily reflective of growth once fully acclimated?

And is there any chance you could slash the number of variables you are testing at a time and do some randomization and replication instead? I know it's very resource intensive and not practical for most folks, but I'm just mentioning it upfront because I don't know your situation and it would strengthen any conclusions from the study a lot. If the answer is no, I get it.

 

[Art]

Subscribed to this thread and bookmarked it to read it again before replying.

 

[Yugang]

so we no longer work together

I really hope you will continue to work together in the future. Hardly anyone in our hobby is experimenting with multiple tanks, and applying as good as possible design of experiment. Both you and _Maq_ have had so much value in doing so. It is also really fun to follow these experiments and place a bet on the outcome

I am not good in water chemistry @Marcel G , but if I understand correctly one critical parameter is which carbon concentration method the plant uses: CO2 versus bicarbonate / soft versus hard water plants. My question is how you chose the 22 ppm HCO3 (is this indeed around dKH 1?), and if you feel this is enough to observe a significant difference with 0 ppm? And then, if the plant indeed consumes the HCO3, will you let it deplete or do you aim to replenish and keep it constant at 22 ppm? Sorry if I totally misunderstood, just trying learn and understand your experiment.

 

[Marcel G]

What are your outcomes and how are you measuring them specifically?

I'm not sure I understand the question. So far, I have tried growing four randomly selected species of aquarium plants based on a recipe suggested by my colleague Maq. Unfortunately, most of the plants tested grew poorly. It must be added, however, that I was occasionally forced to make non-standard interventions due to algae or cyanobacteria invasion. For this reason, I consider these experiments so far to be rather preliminary, test experiments. One experimental set always consisted of four aquariums. The individual aquaria differed from each other basically only in the bicarbonate content (= pH), only the fourth aquarium differed in addition by the increased content of metal cations (K, Mg, Ca) + accompanying anions (sulphates and chlorides). No CO2 was added to any of the aquariums, I used inert silica sand with no supplements, moderate lighting everywhere, maintained room temperature, decent water flow, no filter media, 50% water change each week, very low nutrient concentrations (2 ppm NO3 dosed half as NO3 and NH4, 0.2 ppm H2PO4 etc.), and all microelements exclusively as common salts (unchelated). Virtually the only plant that thrived there was Rotala wallichii (and that was only in the first aquarium, where there were no bicarbonates). All other plants grew more or less poorly. The goal was to see which environment each plant species would thrive best in. The hypothesis was that some plants are acid-loving, others alkaline-loving, and some might do well with increased cation content. Aquarium #1 had a pH of 5.5 (KH=0), aquarium #2 had a pH of 6.5 (KH=0.2), aquarium #3 had a pH of 7.5 (KH=0.9), and aquarium #4 had a pH of 6.5 (KH=0.2). And what was the result? Well, it's hard to say. In the case of R.wallichii, the result was good growth in the first aquarium. In the case of the other plants, the result was rather poor growth. Anyway, I did observe an increase in their biomass, but it is not very telling when most of the plants grew poorly. After the third unsuccessful experiment, I have lost the desire to continue in this mode, so I am thinking of a different approach, and I have reached out to you for comments.

How is the plant material being maintained before the experiment and how will you address the issue that plants often take time to adapt to new conditions, so initial growth in experimental conditions are not necessarily reflective of growth once fully acclimated?

I've tried using in-vitro plants and greenhouse plants. I didn't do any special acclimatization. The main reason was the increased risk of algae overgrowth. Each experiment lasts about 2-3 months. At the latest in the second month the algae start to multiply (often uncontrollably), which is the main problem [not only] of these experiments. When using in-vitro plants, the problems with algae and cyanobacteria were less and occurred later, but they usually take a lot longer to catch on. When using plants from the greenhouse, the algae calamity was usually worse. I tried eliminating the cyanobacteria with antibiotics (worked only partially and for a limited time). I tried eliminating the algae with algaecide, ozone and UV filter. None of these were reliable. Ozone in one case killed almost all my plants. Algaecides at the recommended dosage did not work (but I didn't try all types, of course). The UV filter sometimes worked on the green haze (although usually after a few days), sometimes it didn't work at all, and I had it quite oversized. So, I don't acclimatize because it would prolong the experiment time and the algae would probably come in right from the beginning of the experiment. But since each experiment lasts 2-3 months, I believe that after the first month the plants can be considered acclimatized. Anyway, I am open to any suggestions or recommendations you may have. My goal, of course, is to do the best I can (within my means).

And is there any chance you could slash the number of variables you are testing at a time and do some randomization and replication instead? I know it's very resource intensive and not practical for most folks, but I'm just mentioning it upfront because I don't know your situation and it would strengthen any conclusions from the study a lot. If the answer is no, I get it.

As you rightly point out, such experiments are quite time and money consuming. Of course, I realize that each experiment should be done in at least three repetitions. But I don't have the time, energy, desire nor money to do that. I do what I can given my equipment and financial means. I can't do more. However, it is not a problem for any of you to verify any results if you have any doubts about their predictive value. I don't see your comment as a criticism, but as a perfectly relevant request, I just don't have the capacity to be more rigorous in the methodology of my experiments. So I understand that any potential results will be less relevant as a result. As for limiting the number of variables, at the moment I am deliberately using as wide a range as possible to identify [with a little luck] the main growing methods that would cover the requirements of most plants. This is because I believe that it is hard to do any meaningful experiment if your plants don't grow well in a control aquarium. Therefore, I try to find the "good recipe" first, so that I can then deviate from it in some way in the next steps and investigate the consequences (or pinpoint which of the many parameters in the recipe are key). If you think a different approach would be more appropriate, I would be very happy if you would be willing to share it with me. I'd be happy to think about it.

 

[Marcel G]

I really hope you will continue to work together in the future. Hardly anyone in our hobby is experimenting with multiple tanks, and applying as good as possible design of experiment. Both you and _Maq_ have had so much value in doing so. It is also really fun to follow these experiments and place a bet on the outcome

I do not like to comment on this, but as I wrote to you in our private correspondence, if Maq registers here, I will probably withdraw.

If I understand correctly one critical parameter is which carbon concentration method the plant uses: CO2 versus bicarbonate / soft versus hard water plants. My question is how you chose the 22 ppm HCO3 (is this indeed around dKH 1?), and if you feel this is enough to observe a significant difference with 0 ppm? And then, if the plant indeed consumes the HCO3, will you let it deplete or do you aim to replenish and keep it constant at 22 ppm? Sorry if I totally misunderstood, just trying learn and understand your experiment.

Yes, from what I have read, scientists refer to some plants as "strict CO2 users" while other plants are "bicarbonate users". The question is, do some of those "bicarbonate users" actually require the bicarbonate or will they happily trade it for CO2. Anyway, I also think that while some plants take up nutrients relatively quickly, others take them up more slowly (and grow more slowly as well). However, it may follow that if there is little CO2 in the water (e.g. in low-tech aquariums), then perhaps some plants will not thrive there because they don't get enough CO2 from the water and other (faster) plants suck it away. This is, of course, just speculation that needs to be verified first. That's why I'm trying to collect various plausible possibilities to test. I know (and believe) that Tom Barr has successfully grown a number of plants at high nutrient levels in water. I know (and believe) that Sudipta Shaw (@sudiorca) has successfully grown a number of "challenging" plants without extra CO2 in organic sediment. Some others claim (perhaps truthfully) that a number of their "challenging" plants grow nicely in clean sand. OK, then, let's try to collect all these possibilities and make some basic "test sets" from them that I can better test. But to get back to your question: I picked the 22 ppm HCO3 more or less at random (based on some scientific studies). The problem is that if you don't use extra CO2, then even a tiny concentration of bicarbonate will raise your pH dramatically. That 22 ppm will raise your pH to about 7.5! Unless you are assuming that some plants will welcome a significantly higher pH, I don't think it makes sense to have much more bicarbonate in there. So I suppose the 22 ppm might be enough to test that possibility. But maybe I'm wrong. Please remember that this is just a "suggestion". You're welcome to disagree or suggest other options.

 

[GreggZ]

No CO2 was added to any of the aquariums, I used inert silica sand with no supplements, moderate lighting everywhere, maintained room temperature, decent water flow, no filter media, 50% water change each week, very low nutrient concentrations (2 ppm NO3 dosed half as NO3 and NH4, 0.2 ppm H2PO4 etc.), and all microelements exclusively as common salts (unchelated). Virtually the only plant that thrived there was Rotala wallichii (and that was only in the first aquarium, where there were no bicarbonates).

Curious. Have you tried increasing macro nutrients? Just saying is there a chance that you are assigning a causal effect that doesn't exist? With a focus on limited parameters could you be missing other factors that are in play? Without a nutrient rich substrate could the algae be caused by poor plant growth and plants starving due to low nutrient levels?

 

[Yugang]

I picked the 22 ppm HCO3 more or less at random (based on some scientific studies). The problem is that if you don't use extra CO2, then even a tiny concentration of bicarbonate will raise your pH dramatically. That 22 ppm will raise your pH to about 7.5! Unless you are assuming that some plants will welcome a significantly higher pH, I don't think it makes sense to have much more bicarbonate in there. So I suppose the 22 ppm might be enough to test that possibility. But maybe I'm wrong.

Most likely I am wrong, not you, but I am trying to get to grips with the design of experiment.

Isn't the higher pH, 7.5, what actually happens in nature in hard water environment? And wouldn't we expect this to be lowered a bit when the tank matures, some detritus builds up and some CO2 gets released by microorganisms and life stock so that CO2 is slightly above atmospheric equilibrium of 0.6 ppm? Why would we be worried that plants that evolved for hard water environments couldn't cope with higher pH?

My concern with the experiment, 22 ppm, is that you may be comparing a laboratory super soft water with a still very soft 1 dKH, and that the experiment will not differentiate between super soft and very soft. Perhaps >4 dKH would be my best guess for bicarbonate users, but again I am not very well educated in this.

I found a really interesting article that seems relevant, I attach it in case you have not already seen it. What I learn is that plants that have the capability to use bicarbonates when there is a shortage of CO2, may be happy and more efficient to go for CO2 as carbon source once it becomes available to them. Of course it is really interesting to see if that can be confirmed by your experiment.

 

[ElleDee]

I'm not sure I understand the question.

I mean what are your dependent variable/s. How are you determining which plants are growing best? Plant mass? Some kind of quality ratings for the extent of algae infestation or growth form/color? Vibes?

So far, I have tried growing four randomly selected species of aquarium plants based on a recipe suggested by my colleague Maq. Unfortunately, most of the plants tested grew poorly. It must be added, however, that I was occasionally forced to make non-standard interventions due to algae or cyanobacteria invasion. For this reason, I consider these experiments so far to be rather preliminary, test experiments. One experimental set always consisted of four aquariums. The individual aquaria differed from each other basically only in the bicarbonate content (= pH), only the fourth aquarium differed in addition by the increased content of metal cations (K, Mg, Ca) + accompanying anions (sulphates and chlorides). No CO2 was added to any of the aquariums, I used inert silica sand with no supplements, moderate lighting everywhere, maintained room temperature, decent water flow, no filter media, 50% water change each week, very low nutrient concentrations (2 ppm NO3 dosed half as NO3 and NH4, 0.2 ppm H2PO4 etc.), and all microelements exclusively as common salts (unchelated). Virtually the only plant that thrived there was Rotala wallichii (and that was only in the first aquarium, where there were no bicarbonates). All other plants grew more or less poorly. The goal was to see which environment each plant species would thrive best in. The hypothesis was that some plants are acid-loving, others alkaline-loving, and some might do well with increased cation content. Aquarium #1 had a pH of 5.5 (KH=0), aquarium #2 had a pH of 6.5 (KH=0.2), aquarium #3 had a pH of 7.5 (KH=0.9), and aquarium #4 had a pH of 6.5 (KH=0.2). And what was the result? Well, it's hard to say. In the case of R.wallichii, the result was good growth in the first aquarium. In the case of the other plants, the result was rather poor growth. Anyway, I did observe an increase in their biomass, but it is not very telling when most of the plants grew poorly. After the third unsuccessful experiment, I have lost the desire to continue in this mode, so I am thinking of a different approach, and I have reached out to you for comments.

You know, growing most plants in an inert substrate without supplemental CO2 sounds needlessly challenging to me - and I am a dedicated low tech enthusiast. I've never really seen it done well. I interacted some with Maq at UKAPS and I remember he advocated for silicate sand for a while before changing his mind shortly before he made his exit. He didn't really sell me on it then, though I am always curious about the different methods people employ. Maybe someone will surprise me.

Out of curiosity, besides R. wallichii what were the other species that failed?

I've tried using in-vitro plants and greenhouse plants. I didn't do any special acclimatization. The main reason was the increased risk of algae overgrowth. Each experiment lasts about 2-3 months. At the latest in the second month the algae start to multiply (often uncontrollably), which is the main problem [not only] of these experiments. When using in-vitro plants, the problems with algae and cyanobacteria were less and occurred later, but they usually take a lot longer to catch on. When using plants from the greenhouse, the algae calamity was usually worse. I tried eliminating the cyanobacteria with antibiotics (worked only partially and for a limited time). I tried eliminating the algae with algaecide, ozone and UV filter. None of these were reliable. Ozone in one case killed almost all my plants. Algaecides at the recommended dosage did not work (but I didn't try all types, of course). The UV filter sometimes worked on the green haze (although usually after a few days), sometimes it didn't work at all, and I had it quite oversized. So, I don't acclimatize because it would prolong the experiment time and the algae would probably come in right from the beginning of the experiment. But since each experiment lasts 2-3 months, I believe that after the first month the plants can be considered acclimatized. Anyway, I am open to any suggestions or recommendations you may have. My goal, of course, is to do the best I can (within my means).

Ah, ok, so you aren't starting with submerged growth at all, so every plant will have to convert during the experiment. I've found a lot of plants take longer than that to settle into my tanks, and the speed with which they convert is not very predictive of how they will grow once they are past that initial hurdle. I'm not sure what the answer is though - tricky problem. (I imagine this is much less of an issue with CO2 though.)

As you rightly point out, such experiments are quite time and money consuming. Of course, I realize that each experiment should be done in at least three repetitions. But I don't have the time, energy, desire nor money to do that. I do what I can given my equipment and financial means. I can't do more. However, it is not a problem for any of you to verify any results if you have any doubts about their predictive value. I don't see your comment as a criticism, but as a perfectly relevant request, I just don't have the capacity to be more rigorous in the methodology of my experiments. So I understand that any potential results will be less relevant as a result. As for limiting the number of variables, at the moment I am deliberately using as wide a range as possible to identify [with a little luck] the main growing methods that would cover the requirements of most plants. This is because I believe that it is hard to do any meaningful experiment if your plants don't grow well in a control aquarium. Therefore, I try to find the "good recipe" first, so that I can then deviate from it in some way in the next steps and investigate the consequences (or pinpoint which of the many parameters in the recipe are key). If you think a different approach would be more appropriate, I would be very happy if you would be willing to share it with me. I'd be happy to think about it.

I'm glad you understand what I mean. It would be great if a bored lottery winner would dedicate the resources for a truly rigorous experiment, but it's a high bar to meet without outside funding and a lot of time. Doing the best with what you've got is very reasonable.

This particular test sounds like more of a pre-experiment anyway. In that light, collecting data and measuring outcomes isn't as critical.

 

[Marcel G]

Isn't the higher pH, 7.5, what actually happens in nature in hard water environment? ... Why would we be worried that plants that evolved for hard water environments couldn't cope with higher pH? My concern with the experiment, 22 ppm, is that you may be comparing a laboratory super soft water with a still very soft 1 dKH, and that the experiment will not differentiate between super soft and very soft. Perhaps >4 dKH would be my best guess for bicarbonate users ...

Thank you so much for your comment! Finally some feedback! I've looked at some more articles and I recognize that the 22 ppm (= 0.36 mM) HCO3 concentration I chose is probably too low. In one paper dealing with the appropriate composition of nutrient media for growing submerged aquatic plants, researchers used a concentration of 52 ppm (= 0.85 mM) HCO3 = 2.4°dKH, and considered it a "general-purpose medium". In addition, I found another scientific study where the author reported that some plants (i.e. Elodea canadensis and Ceratophyllum demersum) needed at least 14-19 ppm HCO3 in water with naturally low CO2 concentrations (ranging from 0.4 to 3.1 ppm). Therefore, if they did not have at least this minimum amount in the water, then their growth virtually ceased. So, if I understand correctly, if we want to grow plants in an aquarium without extra CO2, then some plants will probably not grow very well unless we provide them with at least a minimum HCO3 content of at least 1°dKH in the water (but ideally more like 2-3°dKH). So I will try to adjust my recipes 1, 2, 5 and 6 (where I use HCO3) accordingly.

I think we all have the experience of some plants growing well in our aquariums, while others we struggle with (and not infrequently give up on). @Art started a thread here on this, where he asks what plants aquarists have the most problems with. We usually refer to these plants with the term "difficult", "demanding" or "challenging". Their exact list is not important. Just to give two typical examples, Rotala wallichii and Ammannia pedicellata 'Gold' are probably the most frequently mentioned. The question that has been bothering me is why don't these plants usually grow well in our aquariums? What do we have in there that bothers them so much?

Ammannia is usually not a problem if you use an organic substrate and have no bicarbonates in the water (which will cause your pH to drop to 5.5 => water without bicarbonate always has a pH of around 5.5 unless you add some other buffers). But when I tried growing this plant in water without bicarbonates (i.e. with a pH around 5.5), but omitting the organic substrate, it grew poorly. Can anyone think of a reason why? What could the substrate have that is so fundamental that it means the difference between success and failure?

The organic substrate is, of course, a nutrient reservoir. But why isn't the plant growing if we supply all the nutrients it needs in water (and leave out the substrate)? I don't think it's the nutrients alone. I suspect that the problem is probably not the nutrients, but rather the plant.

Maybe (?) this plant is not able to take up some nutrients from the water and simply has to have them in the substrate.

• This option can be tested by keeping all the nutrients in the water in the first aquarium (which corresponds to my recipes #6 or #8), while adding extra organic substrate to the second aquarium (which corresponds to my recipes #2 or #4). If the substrate is the only variable and plants will only grow well in it, then they probably need it (or something in it) to grow well. Later, with further experiments, we can try to better identify this "something" ...

Maybe (?) the organic substrate provides it with more free CO2, which it lacks when growing in sand and without extra CO2 added (and it can't make up the missing carbon from bicarbonate like other plants can).

• This option can be tested by having an inert substrate (sand) in the first aquarium + adding extra CO2 to the water (which corresponds to my recipes #5 or #7), while in the second aquarium I will have an organic substrate, but will not add any extra CO2 to the water (which corresponds to my recipes #2 or #4). If the key factor is the lack of CO2, then the plants should grow well even in sand if they have CO2 in the water ...

Can you think of any other possibilities? If we can pick out any meaningful options, I'll be happy to test them. If you can't help me do that, I can only test what I can think of (which certainly won't cover all the relevant possibilities, since everyone is biased for "their" possibilities).

Therefore, I would again encourage you to share your ideas with me. The fact that my experiments will be preliminary, that no definite conclusions or forms can be drawn from them for the time being ... we don't need to discuss that here. I am aware of that, and my aim here is not to stroke my own ego. Do you want to know what it is that bothers those "challenging" plants in your aquariums? Then try to put on the table some possibility that you think might play a role in that and let's discuss it here. If we find the idea to be reasonable, then I'll be happy to test it out. But without ideas, there's nothing to test. You come up with an idea, the community will challenge it, and I will provide the equipment and arrange a suitable experiment. So that's what I'm offering here, if there's any interest.

 

[Tim Harrison]

I’m definitely interested @Marcel G. As most of us are aware experiments like this will always be difficult to design and manage with scientific rigour, even in a well equipped and resourced lab. Mainly because confounding variables make it difficult to determine causal relationships with a degree of significance.

However, it doesn’t mean it’s not worth trying. I think it’s highly commendable that you are dedicating time and resources to an investigation that has potential to increase knowledge and understanding. And then to also invite us to participate and come along for the ride. For me that’s always going to add up to a worthwhile endeavour.

 

[Marcel G]

Have you tried increasing macro nutrients? Just saying is there a chance that you are assigning a causal effect that doesn't exist?

As you can see in my proposal (see post #1), I am counting on a substantial increase in nutrient concentrations in the next experiment. Precisely because some nutrients may have been in inadequate amounts in those previous experiments.

With a focus on limited parameters could you be missing other factors that are in play?

Of course, I could! That's why I asked for your help. "Two heads are better than one." Perhaps you can come up with a proposal that will bring these factors to light.

Without a nutrient rich substrate could the algae be caused by poor plant growth and plants starving due to low nutrient levels?

I know this is probably a touchy subject here, but I think your question is misleading. In fact, its meaning is similar to asking if plants can be "caused" by low/high nutrient levels. Plants will grow whenever they have adequate (1) light, (2) heat, (3) water and (4) nutrients, and an (5) environment without an excessive amount of disturbance/toxicity (simplistically speaking). Similarly, algae will grow whenever adequate light, heat, water and nutrients are available, and an environment without an excessive amount of disturbance/toxicity. Most of my experiments were designed with different conditions in each aquarium to see which plants would prefer which conditions. It is therefore logical in principle that if a plant would thrive in one set of conditions, it would probably not thrive in the others (where it will naturally suffer). Poor plant growth is therefore hardly avoidable in experiments designed in this way. The algae will simply grow there because they have everything they need. The only way to limit (or prevent) this is to use those "disturbing/toxic influences" => limiting the intensity of lighting, applying downright toxic substances, moving some nutrients from the water to the substrate, introducing enough algae eaters, changing pH, regular maintenance etc. [Algae usually need several weeks to first "pollute" their environment with various metabolites and bacterial biofilms. Only then are they able to "establish" themselves in the environment sufficiently to start multiplying uncontrollably. By regular aquarium maintenance combined with algae eaters, you are constantly "resetting" the environment for them. I highly recommend reading up on this in the scientific literature (e.g. Amazon.com).] But none of these influences can usually be used in an experiment without significantly affecting (biasing) the result. In a conventional aquarium it is a different story. But algae is much harder to deal with in experimental conditions. Try it out and see. Or read any article that deals with submerged aquatic plant testing and you'll find that all scientists face this problem (except they often have equipment that I can't afford). So the idea that you just need to ensure good plant growth and the algae will disappear on its own is, in my opinion, a fallacy (although it is widely held). In fact, this idea completely ignores the huge influence of those "disturbing/toxic influences" that you often have in your aquariums (without perhaps realizing it or attributing such influence to them).

 

[ElleDee]

Oh, I meant to ask before - what are you using for your organic substrate and how are you making sure the nutrients you expect are available?

 

[Marcel G]

What are you using for your organic substrate and how are you making sure the nutrients you expect are available?

I haven't used any organic substrate so far. I plan to use it in my next experiment. I don't know yet which type would be best. Any suggestions?
PS: To make sure it contains all the necessary nutrients, I may consider doing a lab analysis. I've had some types of aquarium substrates analyzed in the past (golias.net). Most soil-baised types would probably contain enought nutrients for couple of months of these preliminary experiments.

 

[Marcel G]

Disclaimer: I would like to point out that I will not be conducting any experiments any time soon. At the moment I am collecting and evaluating information to design the most suitable parameters for each recipe I want to use in the next experiment. I reckon I could start around the end of September/October. One experiment will take approximately 2-3 weeks (depending on the parameters chosen). After that, I'll have some lab analyses entered, which will also take some time. I'm only mentioning this so that you have an idea of what to expect and when to expect from this, if any.