Experiment #6
Lean fertilisation in the water column
Nutrient-poor water + [CO2] + [HCO3] + [substrate]
Main objective
Identify the optimal parameters for cultivation of aquarium plants.
Plants
In this experiment I used the following greenhouse (i.e. emersed-grown) plants:
- Alternanthera reineckii 'Mini'
- Ammannia pedicellata 'Gold' (formerly known as Nesaea …)
- Hygrophila corymbosa
- Rotala wallichii & Rotala sp. 'Vietnam'
Technicalities
Lights
Lighting interval: 8h/day
Light intensity (PAR) in individual aquariums:
| top: | 231 µM/m2·s | → just below the water surface |
| middle: | 98 µM/m2·s | |
| bottom: | 96 µM/m2·s | → at the bottom glass |
Note: there was no difference between the values in the middle vs. at the corners of the aquarium on the horizontal axis (except for the top section = near the light source)
Filtration
A small surface skimmer ensured gentle water movement (circulation) and removed grease from the water surface. Apart from that, I did not use any other kind of filtration.
Temperature
The water in the individual tanks was not heated in any way and was at room temperature (22-25°C).
Substrate
While in the first set (aquaria #1 to #4) ADA Aquasoil Amazonia substrate covered with a layer of pure silica sand was used, in the second set (aquaria #5 to #8) no substrate was used.
1st set → nutrient-rich substrate
- I used the ADA Aquasoil Amazonia substrate (in powder version), which I soaked in tap water for two weeks before starting the experiment.
2nd set → no substrate
- In aquariums with no substrate, I used M16 stainless steel hex nuts inserted into small size (2") hydroponic net pots to anchor (secure) the plants.
Nutrient solutions
Nutrient-poor water
3 ppm NO3, 0.3 ppm PO4, 0.04 ppm Fe
Nutrient-rich substrate
Aquarium #1
pH ~7.2
~10 ppm CO2
Cations
ppm
0.4
NH4+
6.5
Ca2+
2.0
Mg2+
5.1
K+
13.5.0
Na+
Anions
ppm
1.5
NO3−
0.3
H2PO4−
7.9
SO4−
11.6
Cl−
43.6
HCO3−
KH=2
0.04 Fe
Reagents (250 mℓ stock)
μM
mℓ
g
NH4NO3
24
2
2.401
H3PO4
3
0.5
1.729
CaCl2
163
20
2.261
MgSO4*7H2O
82
20
2.526
KHCO3
130
15
2.169
NaHCO3
585
50
2.457
organic substrate
Aquarium #2
pH ~7.5
~4 ppm CO2
Cations
ppm
0.4
NH4+
6.5
Ca2+
2.0
Mg2+
5.1
K+
13.5.0
Na+
Anions
ppm
1.5
NO3−
0.3
H2PO4−
7.9
SO4−
11.6
Cl−
43.6
HCO3−
KH=2
0.04 Fe
Reagents (250 mℓ stock)
μM
mℓ
g
NH4NO3
24
2
2.401
H3PO4
3
0.5
1.729
CaCl2
163
20
2.261
MgSO4*7H2O
82
20
2.526
KHCO3
130
15
2.169
NaHCO3
585
50
2.457
organic substrate
Aquarium #3
pH ~5.2
~10 ppm CO2
Cations
ppm
0.4
NH4+
6.5
Ca2+
2.0
Mg2+
1.6
K+
2.0
Na+
Anions
ppm
1.5
NO3−
0.3
H2PO4−
7.9
SO4−
16.1
Cl−
0.0
HCO3−
KH=0
0.04 Fe
Reagents (250 mℓ stock)
μM
mℓ
g
NH4NO3
24
2
2.401
H3PO4
3
0.5
1.729
CaCl2
163
20
2.261
MgSO4*7H2O
82
20
2.526
KCl
40
5
1.491
NaCl
87
10
1.271
organic substrate
Aquarium #4
pH ~5.5
~4 ppm CO2
Cations
ppm
0.4
NH4+
6.5
Ca2+
2.0
Mg2+
1.6
K+
2.0
Na+
Anions
ppm
1.5
NO3−
0.3
H2PO4−
7.9
SO4−
16.1
Cl−
0.0
HCO3−
KH=0
0.04 Fe
Reagents (250 mℓ stock)
μM
mℓ
g
NH4NO3
24
2
2.401
H3PO4
3
0.5
1.729
CaCl2
163
20
2.261
MgSO4*7H2O
82
20
2.526
KCl
40
5
1.491
NaCl
87
10
1.271
organic substrate
No substrate
Aquarium #5
pH ~7.2
~10 ppm CO2
Cations
ppm
0.4
NH4+
6.5
Ca2+
2.0
Mg2+
5.1
K+
13.5.0
Na+
Anions
ppm
1.5
NO3−
0.3
H2PO4−
7.9
SO4−
11.6
Cl−
43.6
HCO3−
KH=2
0.04 Fe
Reagents (250 mℓ stock)
μM
mℓ
g
NH4NO3
24
2
2.401
H3PO4
3
0.5
1.729
CaCl2
163
20
2.261
MgSO4*7H2O
82
20
2.526
KHCO3
130
15
2.169
NaHCO3
585
50
2.457
no substrate
Aquarium #6
pH ~7.5
~4 ppm CO2
Cations
ppm
0.4
NH4+
6.5
Ca2+
2.0
Mg2+
5.1
K+
13.5.0
Na+
Anions
ppm
1.5
NO3−
0.3
H2PO4−
7.9
SO4−
11.6
Cl−
43.6
HCO3−
KH=2
0.04 Fe
Reagents (250 mℓ stock)
μM
mℓ
g
NH4NO3
24
2
2.401
H3PO4
3
0.5
1.729
CaCl2
163
20
2.261
MgSO4*7H2O
82
20
2.526
KHCO3
130
15
2.169
NaHCO3
585
50
2.457
no substrate
Aquarium #7
pH ~5.2
~10 ppm CO2
Cations
ppm
0.4
NH4+
6.5
Ca2+
2.0
Mg2+
1.6
K+
2.0
Na+
Anions
ppm
1.5
NO3−
0.3
H2PO4−
7.9
SO4−
16.1
Cl−
0.0
HCO3−
KH=0
0.04 Fe
Reagents (250 mℓ stock)
μM
mℓ
g
NH4NO3
24
2
2.401
H3PO4
3
0.5
1.729
CaCl2
163
20
2.261
MgSO4*7H2O
82
20
2.526
KCl
40
5
1.491
NaCl
87
10
1.271
no substrate
Aquarium #8
pH ~5.5
~4 ppm CO2
Cations
ppm
0.4
NH4+
6.5
Ca2+
2.0
Mg2+
1.6
K+
2.0
Na+
Anions
ppm
1.5
NO3−
0.3
H2PO4−
7.9
SO4−
16.1
Cl−
0.0
HCO3−
KH=0
0.04 Fe
Reagents (250 mℓ stock)
μM
mℓ
g
NH4NO3
24
2
2.401
H3PO4
3
0.5
1.729
CaCl2
163
20
2.261
MgSO4*7H2O
82
20
2.526
KCl
40
5
1.491
NaCl
87
10
1.271
no substrate
- Water flow ensured by a surface skimmer (Jingye JY-350)
- no filtration used
- Water changes done once a week (with 50% of the water changed) with macro-nutrients replenishment
- Micro-nutrients added every other day
Weekly amount of microelements (divided into three doses):
- Fe/DTPA = 0.04 ppm (+ 0.02 ppm Fe/gluconate)
- Mn/EDTA = 0.02 ppm
- B = 0.01 ppm
- Zn/EDTA = 0.006 ppm
- Cu/EDTA = 0.002 ppm
- Co/EDTA = 0.00002 ppm
- Mo = not added
- Carbon dioxide
- Extra CO₂ added to aquaria #1, #3, #5 and #7 using a simple glass diffuser, the function and parameters of which are described in more detail in a separate article
- CO₂ concentration in these aquaria: ≈10 ppm
- No extra CO₂ added to aquaria #2, #4, #6 and #8
- CO₂ concentration in these aquaria: ≈4 ppm
CO₂ concentration measured by Carbon Dioxide Chemical Test Kit (Hanna HI3818), which should give similar results to a professional CO₂ meter (OxyGuard) → see 2hraquarist.com.
Hanna CO2 chemical test kit HI3818 - Extra CO₂ added to aquaria #1, #3, #5 and #7 using a simple glass diffuser, the function and parameters of which are described in more detail in a separate article
Documentation
Week #1 (day #5)
#1
Substrate
HCO3−
CO2
pH 6.0
#2
Substrate
HCO3−
CO2
pH 6.9
#3
Substrate
HCO3−
CO2
pH 5.3
#4
Substrate
HCO3−
CO2
pH 6.2
#5
Substrate
HCO3−
CO2
pH 5.8
#6
Substrate
HCO3−
CO2
pH 7.1
#7
Substrate
HCO3−
CO2
pH 4.4
#8
Substrate
HCO3−
CO2
pH 6.5
- All plants arrived in excellent condition
Week #3 (day #18)
#1
Substrate
HCO3−
CO2
pH 6.8
#2
Substrate
HCO3−
CO2
pH 7.4
#3
Substrate
HCO3−
CO2
pH 6.0
#4
Substrate
HCO3−
CO2
pH 6.4
#5
Substrate
HCO3−
CO2
pH 7.3
#6
Substrate
HCO3−
CO2
pH 8.0
#7
Substrate
HCO3−
CO2
pH 4.9
#8
Substrate
HCO3−
CO2
pH 5.5
- Algae
- most of them are in the 1st set (= substrate)
- Alternanthera reineckii 'Mini'
- in all aquariums with CO₂ it is bigger and seems to be in better condition and with richer colours
- key to the rating below: #1 = tank number, (1)(2)(3)(4) = mark/grade from best (1) to worst (4), (?) = hard to say
- 1st set
- #1: (1) largest and visually in good shape (straight & thick leaves, rich colour)
- #2: (4) visually in worst shape (smallest, faint colour, largest leaf deformation of the first set)
- #3: (2) visually in good shape (straight & thick leaves, richest colour), but smaller than in aquarium #1
- #4: (3) slow growth
- 2nd set
- #5: (3) visually in fair shape (slightly deformed leaves, fainter colour), but slightly smaller than in aquarium #8
- #6: (4) visually in worst shape of the second set (smallest, mild leaf deformation, fainter colour, hardly any growth)
- #7: (1-2) visually in moderately good shape (slightly deformed leaves, but rich colour)
- #8: (1-2) visually in fair shape (slightly deformed leaves, fainter colour)
- Ammannia pedicellata 'Gold'
- it's hard to say in which aquarium [this plant] is in the best shape; it's about the same size in all of them and seems to have problems everywhere (except for aquarium #7)
- 1st set
- in the whole 1st set (= in the substrate) it has stunted growth tops
- since it seems fine in aquarium #7 (nice straight leaves, no stunted growth tops), the substrate [among other things] may be to blame
- 2nd set
- #5: (4) visually worst condition of the second set (stunted growth tops, newer leaves deformed)
- #6: (?) visually in somewhat poorer condition (slight stunting of growth tips)
- #7: (1) visually in the best condition of all aquariums (straight leaves, no signs of stunting, rich colour)
- #8: (?) visually in acceptable condition (slight signs of stunting, slightly more pale colour)
- Hygrophila corymbosa
- in all aquariums with CO₂ it is bigger and visually in better shape and with richer colours
- 1st set
- #1: (2) visually in good shape, but significantly smaller than in aquarium #3
- #2: (3) visually the same as when planted (hardly any growth, but no necrosis)
- #3: (1) largest and visually in the best shape of the first set
- #4: (4) visually in bad shape (stagnation, leaves do not open to light, necrosis, dying)
- 2nd set
- #5: (2) visually in good shape, but slightly smaller than in aquarium #7
- #6: (4) visually the same as when planted, but its condition is deteriorating (stagnation, hardly any growth, faint colour, algae [probably diatoms] settle on the leaves)
- #7: (1) largest and visually in good shape
- #8: (3) visually in bad shape (leaves do not open to light, slightly deformed leaves, fainter colour, but slightly larger than in aquarium #6)
- Rotala sp. 'Vietnam' (Rotala wallichii)
- in all aquariums with CO₂ it is [much] bigger and seems to be in better shape
- 1st set
- #1: (2) visually in good shape, almost as tall as in aquarium #3
- #2: (?) visually in good shape, but smaller (unfortunately most of the stems are R.wallichii, not R.Vietnam, so they cannot be compared with other aquariums)
- #3: (1) largest and visually in good shape
- #4: (3-4) ambiguous (multivalent) condition
- 2nd set
- #5: (2) visually in good shape
- #6: (3-4) visually in good shape, but much smaller; about half of the stems are R.wallichii and the other half R.Vietnam
- #7: (1) visually in good shape
- #8: (3-4) visually in good shape, but much smaller; about half of the stems are R.wallichii and the other half R.Vietnam
Week #5 (day #31)
#1
Substrate
HCO3−
CO2
pH 6.4
#2
Substrate
HCO3−
CO2
pH 6.7
#3
Substrate
HCO3−
CO2
pH 5.2
#4
Substrate
HCO3−
CO2
pH 5.3
#5
Substrate
HCO3−
CO2
pH 6.8
#6
Substrate
HCO3−
CO2
pH 7.4
#7
Substrate
HCO3−
CO2
pH 4.4
#8
Substrate
HCO3−
CO2
pH 4.8
- Alternanthera reineckii 'Mini'
- 1st set
- #1: largest, outwardly in good condition, but the upper leaves have some algae
- deficient [K], toxic [Mn(575)] → see laboratory analysis results
- deficient [K], toxic [Mn(575)] → see laboratory analysis results
- #2: <no comment>
- #3: healthy-looking, straight leaves, but stunted growth tips
- deficient [K], toxic [Mn(772), Zn(172)] → see laboratory analysis results
- deficient [K], toxic [Mn(772), Zn(172)] → see laboratory analysis results
- #4: <no comment>
- #1: largest, outwardly in good condition, but the upper leaves have some algae
- 2nd set
- #5: [plants] removed due to extensive chlorosis
- deficient [K], toxic [Fe(669), Zn(185)] → see laboratory analysis results
- deficient [K], toxic [Fe(669), Zn(185)] → see laboratory analysis results
- #6: [plants] removed due to extensive chlorosis
- #7: <no comment>
- #8: <no comment>
- #5: [plants] removed due to extensive chlorosis
- 1st set
- Ammannia pedicellata 'Gold'
- 1st set
- #1: <no comment>
- <not analyzed>
- <not analyzed>
- #2: <no comment>
- <not analyzed>
- <not analyzed>
- #3: probably a slight improvement
- excessive [Cu], toxic [Fe(507), Mn(1271)] → see laboratory analysis results
- excessive [Cu], toxic [Fe(507), Mn(1271)] → see laboratory analysis results
- #4: <no comment>
- <not analyzed>
- <not analyzed>
- #1: <no comment>
- 2nd set
- #5: <no comment>
- <not analyzed>
- <not analyzed>
- #6: <no comment>
- <not analyzed>
- <not analyzed>
- #7: outwardly in the best condition
- excessive [Mn], toxic [Zn(205)] → see laboratory analysis results
- excessive [Mn], toxic [Zn(205)] → see laboratory analysis results
- #8: <no comment>
- <not analyzed>
- <not analyzed>
- #5: <no comment>
- 1st set
- Hygrophila corymbosa
- 1st set
- #1: [plants] removed from the aquarium because they have grown to the surface
- #2: <no comment>
- #3: [plants] removed from the aquarium because they have grown to the surface
- #4: <no comment>
- 2nd set
- #5: [one of the two plant stems] removed from the aquarium because it has grown to the surface
- #6: <no comment>
- #7: [plants] removed from the aquarium because they have grown to the surface
- deficient [K], excessive [Ca, Zn, Cu] → see laboratory analysis results
<picture-missing>
- deficient [K], excessive [Ca, Zn, Cu] → see laboratory analysis results
- #8: <no comment>
- 1st set
- Rotala sp. 'Vietnam' (Rotala wallichii)
- 1st set
- #1: [plants] removed from the aquarium because they have grown to the surface
- #2: <no comment>
- <not analyzed>
- <not analyzed>
- #3: [plants] removed from the aquarium because they have grown to the surface
- #4: <no comment>
- <not analyzed>
- <not analyzed>
- 2nd set
- #5: <no comment>
- <not analyzed>
- <not analyzed>
- #6: mild chlorosis
- <not analyzed>
- <not analyzed>
- #7: [plants] removed from the aquarium because they have grown to the surface
- #8: <no comment>
- <not analyzed>
- <not analyzed>
- #5: <no comment>
- 1st set
Results
Note: In the first weeks a brown haze was visible in the first experimental set (from leached humic substances from freshly flooded substrate).
Subjective assessment
The following data is a brief description of the visual condition of the plants in each aquarium (1 to 8). Green indicates best condition, blue indicates good condition and red indicates fair condition.
Alternanthera reineckii 'Mini'
- soil + CO₂ + HCO3 + pH 6.5 = good shape, largest, but later deteriorating + algae
- soil − CO₂ + HCO3 + pH 7.0 = bad shape
- soil + CO₂ − HCO3 + pH 5.5 = good shape, but smaller than #1, later partially stunted
- soil − CO₂ − HCO3 + pH 6.0 = fair shape, but slow growth
- + CO₂ + HCO3 + pH 7.0 = initially fair shape, later extensive chlorosis
- − CO₂ + HCO3 + pH 7.5 = bad shape, later extensive chlorosis
- + CO₂ − HCO3 + pH 4.5 = moderately good shape, later best shape
- − CO₂ − HCO3 + pH 5.5 = fair shape
Ammannia pedicellata 'Gold'
- soil + CO₂ + HCO3 + pH 6.5 = stunted, later cyanobacteria on upper leaves
- soil − CO₂ + HCO3 + pH 7.0 = stunted, later cyanobacteria on upper leaves
- soil + CO₂ − HCO3 + pH 5.5 = stunted, later slight improvement, but hair algae on leaves
- soil − CO₂ − HCO3 + pH 6.0 = stunted, hardly any growth, later hair algae on leaves
- + CO₂ + HCO3 + pH 7.0 = stunted, but almost algae-free
- − CO₂ + HCO3 + pH 7.5 = stunted, later cyanobacteria on upper leaves
- + CO₂ − HCO3 + pH 4.5 = best shape, almost algae-free
- − CO₂ − HCO3 + pH 5.5 = acceptable shape, slow growth, later some hair algae
Rotala sp. 'Vietnam'
- soil + CO₂ + HCO3 + pH 6.5 = best shape, largest
- soil − CO₂ + HCO3 + pH 7.0 = initially good shape, but smaller, later bad shape + algae
- soil + CO₂ − HCO3 + pH 5.5 = best shape, largest
- soil − CO₂ − HCO3 + pH 6.0 = ambiguous shape
- + CO₂ + HCO3 + pH 7.0 = good shape, large
- − CO₂ + HCO3 + pH 7.5 = rather bad shape, smaller + mild chlorosis
- + CO₂ − HCO3 + pH 4.5 = best shape, largest
- − CO₂ − HCO3 + pH 5.5 = good shape, but much smaller
Hygrophila corymbosa
- soil + CO₂ + HCO3 + pH 6.5 = good shape, but significantly smaller than #3
- soil − CO₂ + HCO3 + pH 7.0 = hardly any growth
- soil + CO₂ − HCO3 + pH 5.5 = best shape (of the 1st set), largest
- soil − CO₂ − HCO3 + pH 6.0 = bad shape
- + CO₂ + HCO3 + pH 7.0 = good shape, but slightly smaller than #7
- − CO₂ + HCO3 + pH 7.5 = hardly any growth, deteriorating shape
- + CO₂ − HCO3 + pH 4.5 = best shape (of the 2nd set), largest
- − CO₂ − HCO3 + pH 5.5 = bad shape
Objective data
| Legend: | % | ppm | |||||||||||||
| State | C | N | P | K | Ca | Mg | S | Na | Cl | Fe | Mn | B | Zn | Cu | Mo |
| Deficiency | less than normal | ||||||||||||||
| Sufficiency | 35-45 | 2-4 | 0.2-0.7 | 1-3 | 0.5-2.0 | 0.1-0.5 | 0.15-0.5 | ? | 0.05-0.3 | 75-400 | 20-300 | 10-50 | 20-100 | 2-20 | 0.2-10 |
| Excess | slightly more than normal | ||||||||||||||
| Toxicity | significantly more than normal | ||||||||||||||
Notes:
- The ranges of deficiency, sufficiency (normal), and excess (toxicity) were taken from data applicable to terrestrial plants and adapted for aquatic plants using artificial intelligence (taking into account their physiological differences). However, I would like to point out that there is not any definitive standard (norm) for freshwater aquatic plants, so all I can offer is but a qualified estimate. I leave it up to the reader to evaluate and interpret this data in their own way.
- Where I had sufficient new material available, I used only this new material for analysis. In exceptional cases (e.g., Ammannia), I also used some of the old material (i.e., original leaves/stems). However, I never used roots.
Alternanthera reineckii 'Mini'
6.1. + 6.5 → (14)-5-7-2 mg/ℓ (Na):K:Ca:Mg, 3-0.3 mg/ℓ NO3:PO4, 60:20 µg/ℓ Fe:Mn + 10 mg/ℓ CO2 + KH=2
6.3 + 6.7 → (12)-2-7-2 mg/ℓ (Na):K:Ca:Mg, 3-0.3 mg/ℓ NO3:PO4, 60:20 µg/ℓ Fe:Mn + 10 mg/ℓ CO2 + KH=0
| % | ppm | ||||||||||||
| Tank | C | N | P | K | Ca | Mg | Na | Fe | Mn | Zn | Cu | ||
| 6.1 | 38.55 | 4.80 | 0.53 | 0.03 ? | 0.77 | 0.59 | 0.33 | 319 | 575 | 144 | 16 |  |
 |
| 6.3 | 39.06 | 5.29 | 0.54 | 0.03 ? | 0.60 | 0.34 | 0.06 | 390 | 772 | 172 | 15 | |
|
| 6.5 | 37.35 | 3.71 | 0.43 | 0.05 ? | 1.56 | 1.18 | 0.31 | 669 | 165 | 185 | 11 | |
|
| 6.7 | 40.02 | 3.38 | 0.47 | 0.03 ? | 0.48 | 0.60 | 0.05 | 287 | 169 | 151 | 15 | |
|
? = Questionable result (error)
Ammannia pedicellata 'Gold'
6.3 + 6.7 → (12)-2-7-2 mg/ℓ (Na):K:Ca:Mg, 3-0.3 mg/ℓ NO3:PO4, 60:20 µg/ℓ Fe:Mn + 10 mg/ℓ CO2 + KH=0
| % | ppm | ||||||||||||
| Tank | C | N | P | K | Ca | Mg | Na | Fe | Mn | Zn | Cu | |
|
| 6.3 | 40.61 | 3.68 | 0.62 | 2.67 | 1.98 | 0.69 | 0.92 | 507 | 1271 | 126 | 22 | |
|
| 6.7 | 41.06 | 2.79 | 0.46 | 1.91 | 1.78 | 0.77 | 0.86 | 318 | 348 | 205 | 18 | |
|
Hygrophila corymbosa
6.3 + 6.7 → (12)-2-7-2 mg/ℓ (Na):K:Ca:Mg, 3-0.3 mg/ℓ NO3:PO4, 60:20 µg/ℓ Fe:Mn + 10 mg/ℓ CO2 + KH=0
| % | ppm | ||||||||||||
| Tank | C | N | P | K | Ca | Mg | Na | Fe | Mn | Zn | Cu | |
|
| 6.7 | 35.99 | 3.38 | 0.32 | 0.09 ? | 4.62 | 0.72 | 0.62 | 150 | 113 | 160 | 23 | |
|
? = Questionable result (error)
Rotala wallichii
<n/a>
My commentary & interpretation
Disclaimer: My commentary and interpretation is based on the assumption that the ranges for deficient, normal, and excessive/toxic concentrations of nutrients in plant dry matter [taken from materials applicable to terrestrial plants] are most likely also valid for aquatic plants. If this assumption proves to be incorrect, then of course the conclusions I draw from it here would not apply either.
As with the previous experiment, it seems that CO2 is the biggest guarantee of success.
- It gives clearly the best results for all [tested] plants.
- This suggests that [even with lean fertilisation in the water column] carbon (C) remains the most limiting element in our aquariums.
- While some submerged plants requiring CO2 (i.e. the so-called „strict/obligate CO2 users“) can get by with naturally low concentrations of carbon dioxide (<5 ppm), others [seem to] require slightly higher concentrations (5-10 ppm).
Based on the above data, the poor plant condition seems to stem from micronutrient toxicity (particularly Fe/Mn/Zn). The question is how to explain (interpret) this.
The parameters of individual aquariums can provide some guidance for interpretation:
In experiment #5, higher nutrient concentrations were used:
- 10 ppm NO3 + 1.5 ppm NH4
- 2 ppm PO4
- 20-6-5 ppm Ca-Mg-K
- 14 ppm Na
- 0.2 ppm Fe …
In experiment #6, lower nutrient concentrations were used:
- 1.5 ppm NO3 + 0.4 ppm NH4
- 0.3 ppm PO4
- 7-2-2 ppm Ca-Mg-K
- 2 ppm Na
- 0.04 ppm Fe …
In addition, I used organic substrate (= source of additional nutrients and organics) in aquariums #1-4 and bicarbonates (HCO3) in aquariums #1-2 and #5-6.
Potassium (K) deficiency ← note on its improbability
- Deficiency: <1.0% K in dry matter
- Sufficiency: 1.2-7.0% K
- Problematic cases:
- Alternanthera reineckii: 0.03% K (all tanks)
- Hygrophila corymbosa: 0.06-0.09% K (all tanks)
- Possible explanations:
- Potassium leakage in the aquarium due to severe tissue damage or stress
- Potassium leakage caused by improper preparation of the sample for laboratory analysis
- Lab error during analysis
Micronutrient toxicity
Iron (Fe) toxicity
- Sufficiency: 75-400 ppm Fe
- Toxicity: >500 ppm Fe in dry matter
- Toxic cases:
- Rotala wallichii: 3,721 ppm Fe (Exp. 5, Tank 5) - extreme toxicity
- Ammannia pedicellata: 1,014 ppm Fe (Exp. 5, Tank 7), 507 ppm Fe (Exp. 6, Tank 3) - extreme to moderate toxicity
Manganese (Mn) toxicity
- Sufficiency: 20-300 ppm Mn
- Toxicity: >400 ppm Mn in dry matter
- Toxic cases:
- Ammannia pedicellata: 1,271 ppm Mn (Exp. 6, Tank 3) - extreme toxicity
- Alternanthera reineckii: 772 ppm Mn (Exp. 6, Tank 3) - severe toxicity
Zinc (Zn) toxicity
- Sufficiency: 20-100 ppm Mn
- Toxicity: >200 ppm Zn in dry matter (>150 ppm in sensitive species)
- Toxic cases:
- Alternanthera reineckii: 172-185 ppm Zn (Exp. 6, Tanks 3 & 5) - mild toxicity
- Ammannia pedicellata: 205 ppm Zn (Exp. 6, Tank 7) - mild toxicity
- Hygrophila corymbosa: 206 ppm Zn (Exp. 5, Tank 5) - mild toxicity
- Possible explanations:
- Chelate instability and breakdown
- Hyperaccumulation mechanism
- Poor regulatory ability
- Detrimental effect of bicarbonate and/or organic substrate
Probable characteristics of individual species → hypothesis
Alternanthera reineckii 'Mini'
Mesotrophic species (?)
- (1) bicarbonate (HCO3) sensitive
- (1) phosphate (PO4) sensitive
- (3) organic substrate sensitive
- (4) <unknown µ sensitivity> → needs further testing
Ammannia pedicellata 'Gold'
Oligotrophic species
- (1) bicarbonate (HCO3) sensitive
- (1) phosphate (PO4) sensitive
- (3) organic substrate sensitive
- (4) µ ultra-sensitive
- (5) efficient µ uptaker (hyper-accumulator) with poor regulatory ability
Hygrophila corymbosa
(Hyper)eutrophic species
- (1) bicarbonate (HCO3) tolerant
- (1) phosphate (PO4) tolerant
- (3) organic substrate tolerant
- (4) µ tolerant
Rotala wallichii
Oligotrophic species
- (1) bicarbonate (HCO3) sensitive
- (1) phosphate (PO4) sensitive
- (3) organic substrate sensitive
- (4) µ sensitive
- (5) ultra-efficient µ uptaker (hyper-accumulator) with poor regulatory ability
- (6) CO2 undemanding ← can cope with naturally low CO2 levels