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Rotala wallichii: growth experiment

Some hobbyists have no problem growing this plant while others can't grow it well no matter what they try to do.

There is an extensive journal describing the (so far) unsuccessful efforts of one such hobbyist - Pikez.
You can find it on BarrReport (http://www.barrreport.com/forum/barr-report/aquascaping/223782-going-dutch-with-aquasoil).

Some hobbyists think that growing aquarium plants is as simple as to provide a nutrient rich substrate, plenty of light, more ferts than one plant will ever need, and just enough CO2 as not to kill your fish. Change water on day 7, clean filter once a month and repeat.

Is this really as easy?
Does this apply to all plants?

1) Let me acquaint you in brief with my growth experiment:

Test #1:



Day #10:


Day #18:


Parameters:
- Substrate: plain sand
- Nutrients: 2, 4, 8, 16, 32 ppm NO3 in tank #1 to #5 (10x less PO4, 100x less Fe-DTPA + other essential nutrients)
- Light: 100 µmol PAR at substrate level, 200 µmol PAR at water surface
- Water: 3°dKH (61 ppm HCO3), 6°dGH (25 ppm Ca + 9 ppm Mg)
- CO2: 35-45 ppm (pH 6.35 to 6.45)
- Flow: moderate
- Water change: 100% each week (same with the following tests)
- Dosing frequency: right after the water change (i.e. once a week)

Test #2:



Parameters (exactly the same as in Test #1)
- Substrate: plain sand
- Nutrients: 2, 4, 8, 16, 32 ppm NO3 in tank #1 to #5 (10x less PO4, 100x less Fe-DTPA + other essential nutrients)
- Light: 100 µmol PAR at substrate level, 200 µmol PAR at water surface
- Water: 3°dKH (61 ppm HCO3), 6°dGH (25 ppm Ca + 9 ppm Mg)
- CO2: 35-45 ppm (pH 6.35 to 6.45)
- Flow: moderate

Test #3:



Parameters:
- Substrate: plain sand (except tank #2)
- Macro nutrients: 20 ppm NO3, 2 ppm PO4, 12.5 ppm K, 96 ppm SO4, 46 ppm Na in all tanks
- Micro nutrients: 0.5 ppm Fe-DTPA, 0.13 ppm Mn, 0.06 B in all tanks except tank #4
- Extra: soil substrate in tank #2, DOM in tank #3, low micro in tank #4 (0.02 ppm Fe-DTPA, 0.005 ppm Mn, 0.0025 ppm B + other essential nutrients)
- Light: 100 µmol PAR at substrate level, 200 µmol PAR at water surface
- Water: 3°dKH (61 ppm HCO3), 6°dGH (25 ppm Ca + 9 ppm Mg)
- CO2: 35-45 ppm (pH 6.35 to 6.45)
- Flow: moderate

Test #4:



Parameters:
- Substrate: plain sand (except tank #2)
- Macro nutrients: tank #1: 2 ppm NO3, 0.2 ppm PO4, 1.25 ppm K; tanks #2-5: 20 ppm NO3, 2 ppm PO4, 12.5 ppm K;
tanks #1-5: 288 ppm SO4, 139 ppm Na
- Micro nutrients: 0.5 ppm Fe-DTPA, 0.13 ppm Mn, 0.06 B (except tanks #1 and #4)
- Extra: soil substrate in tank #2, DOM in tank #3, low macro in tank #1, low micro in tank #1+4 (0.02 ppm Fe-DTPA, 0.005 ppm Mn, 0.0025 ppm B + other essential nutrients)
- Light: 100 µmol PAR at substrate level, 200 µmol PAR at water surface
- Water: 9°dKH (184 ppm HCO3), 11°dGH (75 ppm Ca + 27 ppm Mg)
- CO2: 35-45 ppm
- Flow: moderate

Short experiment evaluation:
From the above tests it seems that the Rotala wallichii grew best in the following conditions:

  • Soft water with low alkalinity and very low nutrient levels in water column (see tests #1+2: tank #1)
  • Soft water with low alkalinity, high levels of macro, but very low levels of micro in water column (see test #3: tank #4)
  • Hard water with high alkalinity with very low nutrient levels in water column (see test #4: tank #1)

Also, the higher the nutrient levels in water column, the worst the plant condition under the given conditions.
None of the above tests give me the awaited results (i.e. perfectly healthy plants in very good condition and red/pink coloration). I would like to continue further with this experiment. Hopefully, we will get to the desired results one day, and know the true demands of this sensitive aquarium plant species from Lythraceae family.

2) Let me cite what Pikez says on BarrReport to this:

Post #453:

→ So, how do you explain that? How can Tom [Barr] make it grow in a "high-ferts environment"?
→ I have no idea. I know at least 3 people (besides Tom) who grow wallichii really well with full EI fert levels.
→ I also have no idea why wallichii did increasingly poorly as nutrient levels increased in Marcel Golias' experiments. The experiments were well conducted and even duplicated. Both times, the higher the nutrients, the worse the plant looked. Poor growth is correlated to increased nutrients, but the experiment design is not capable of establishing causality or answering WHY exactly it happened. That may have to be a series of future experiments.

Post #460:

→ All plants have a 'comfy range' where they thrive. People who tell you that Rotala wallichii is a piece of cake to grow and that you should 'just fix your CO2', may have accidentally stumbled onto the ideal range for that plant. Old school hobbyists with low-light dirtied tanks do better with it than those with high-tech tanks. It's more complicated than just fixing CO2, which I'm sure is a contributing factor.
→ Most plants have a wide range where they thrive. Wallichii appears to have a narrow range, as shown by Marcel's repeated experiments. I don't know how (or am unwilling to repeat my detox experience) to recreate that narrow range. But in the absence of all facts, it is fair to say that the plant is more likely to thrive where the nutrients are lower than higher.

Post #477:

→ In Marcel Golias' experiments, wallichii started showing signs of acute toxicity at:
NO3 = 4 ppm
P = 0.4 ppm
Fe = 0.04 ppm
Mn 0.01 ppm
B = 0.005
Cu = 0.002
Zn = 0.002
Mo = 0.0005
→ However it did fine at half the above dosage level. But it progressively got worse (hyper-sensitive) as the nutrient level increased.
It is clearly acute toxicity. You cannot interpret it as anything else. The symptoms were deformed tips, loss of color, longer internodes, and slower growth. These are all standard issue Lythraceae problems that many of us have. It is not limited to wallichii, but exaggerated in this species.
→ The obvious question is, why does this not happen in many tanks with higher nutrient levels. The only (and somewhat inadequate) theory is that there is something in actual tanks with established filters, substrate, live stock, other plants, higher volume, etc. that suppresses this hyper-sensitivity. We do not know WHAT suppresses it. And we do not know which one of the 8 nutrients above is causing the issue.
→ It's not that toxicity does not exist or does not occur in many EI tanks. It is most likely that there are strong mitigating factors helping the plant overcome the toxicity.
→ We don't have a clue what those mitigating factors are. Until we conclusively do, toxicity (trace, macro, or both) has to remain on the table as a potential cause of plant troubles. Any counter argument must be accompanied with equally compelling scientific evidence. It's a shame that there aren't more people conducting controlled experiments like Marcel.
→ Ah, the ghost of the now-silent Solcielo Lawrencia.*

* (Solcielo stopped posting on BarrReport after Tom Barr rescinded his moderator status as Tom was upset that Lawrence was talking about toxicity, and besides that was saying that plants can grow fine with low CO2 even under high light intensities).

Post #573:

→ To truly understand what makes a species grow, we need to be able to define what makes it grow as well as what makes it not. Most of us stumble upon a tank environment that is suited to a particular species. Sometimes that condition is narrow and ideal for a 'difficult' plant. That does not make us an expert. We just got lucky. Increasing CO2, lowering KH, having about 100 PAR, good circulation, rich substrate, adequate (but no more or less) ferts, all increase 'luck.' But these conditions do not define the specifics. These are broadly favorable conditions.
→ There is no 'easy' or 'difficult' plant. All plants have specific conditions under which they will grow like weeds. For some species, required conditions are broad. For others, not.
To be able to truly learn about growing plants, you need to be able to cast aside dogma and question everything. Just because I have a journal here on Barr Report, does not mean I adhere closely to EI principles. EI has taught me a LOT about horticulture. My main complaint about EI is that it's a broad brush approach and prone to user-error. I am driven by scientific curiosity (for both work and hobbies) and sharing my lessons here is what I find fun, warts, struggles and all, even the algae attacks, melting, tip stunting, failed experiments, and disasters.
→ With my current tank, I have more 'luck' with more than average: CO2, circulation, water changes. And more 'luck' with less than average: traces, light, plant mass.

3) Now let me suggest a hypothesis to test:

Question: "If the above test results are valid, how then do you explain that some hobbyists can grow Rotala wallichii in EI tanks with high nutrient levels?"

If the above experiment shows that with high nutrients in water column the Rotala wallichii's condition get worse, how is it that in some nutrient-rich tanks it can grow well?

I don't have a definitive answer that have been verified by a controlled experiment, but there are some possible explanations waiting to be verified by whomever wants to seize the opportunity.

You may know from chemistry lessons that at higher concentration (or temperature) the chemical reactions take place at much faster rate and with more intensity. So it may very well be that at very high nutrient levels, some reactions take place in your tank in much higher rate and intensity, which would not happen under lower nutrient concentrations (or with less intensity only). The usual suspects here are phosphates and iron. These can precipitate very quickly if both are in very high concentrations in water column. And you need not even know this happened. You will think that what helped your sensitive plants to grow better were these higher nutrient levels, while in fact it could very well be the exact opposite (i.e. at higher concentrations some nutrients reacted and precipitated, thus their concentration dropped to nearly zero which helped your plants to stay away from their toxic effects and grow better). This is only a speculation on my side, but one that should be considered.

Another possible explanation that comes to my mind is the "protective effect" of higher calcium (Ca) or dissolved organic carbon (DOM) content in water column. There are many scientific papers with clear evidences of high Ca levels protecting fishes from metal toxicity. Dissolved organic carbon (DOM) is known to bind heavy metals in water column. So if you have some DOM in your water, and dose some heavy metals into it, the metals may bind to the DOM. What does it mean for your plants? In case you dose the heavy metals in high amounts into your water, and there is no DOM, your plants will be exposed to toxic levels of these "nutrients". But in case you have DOM there, the metals may bind onto it, so that you will have nearly no dissolved metals in your tank water. The metals will be released from the DOM over time, but in a slow way, which means that you'll have much lower minute concentration of these metals in your water. The toxicity of metals depends greatly on their forms of occurrence. Simple ionic forms are usually much more toxic, while the complexed forms are less harmful.

There are many chemical reactions (like precipitation, oxidation, reduction, sorption, desorption, etc.) that take place under different conditions. Different substrates can adsorb nutrients in different manner also. Photochemical reactions may affect the degradation of chelates and nutrient releasing also. For example, forms of occurrence of dissolved and undissolved iron in waters depends on the pH, redox potential and complexing substances present in the water. In oxic conditions a rufous precipitate [hydrated ferric oxide or amorphous FeO(OH)] forms - and therefore it is possible to maintain/keep only very low concentrations of trully dissolved iron in water (typically below about 60 µg/ℓ = 60 ppb), where inorganic or organic complexing agents (such as humic substances or chelates) are absent. So, oxygen, redox, temperature, light intensity, pH, DOM and probably many other factors play a role in nutrients availability (and their potential toxicity). Every plant scientist will tell you this, but some people in our hobby seem to ignore these facts. And this obviously does not help our hobby to advance in the least.

So from the above data you can now better understand why each tank is unique, and why we can't draw a universally valid conclusions for all hobbysts just from one planted tank. That something works in one tank does not mean that it must work in other tanks, if all the conditions are not the same. So if someone adds 10 ppm PO4 and 2.5 ppm Fe into his tank, and sees no toxic effects on his plants, does not mean that if you add the same amounts into your tank you won't experience a disaster. My controlled experiments shows that the higher the nutrient levels in water column, the worst the plant condition under the given conditions. But it's possible you won't see the same results if you have different conditions in your tank. To understand how different conditions affect the chemical reactions and availability (or toxicity) of our nutrients is the key to systematic (universally valid) success.

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A final note:

By this post I would like to share what I had found out in my controlled experiments. I describe it extensively on my Czech website with much more pictures, tables, charts, etc., but I understand that Google Translate plug-in does not do the best job in translating all the nuances of my words. If anyone is interested in more details, he/she can contact me through a personal message here or by email. I won't reply to any questions publically here in the forum, as I'm not compatible with this kind of discussion, and easily get banned (as on BarrReport.com and TPT.net already).

Marcel G
 
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