This article will probably be a bit more complicated to understand and follow for ordinary aquarists without a biological background, who are not close to scientific experiments.
I will therefore try to explain briefly what is going on here. The point is to find out whether it makes sense to fertilize the plants at all, and if so, how much.
In other words, I will try to find out which nutrient doses are insufficient for different types of plants, which are optimal, which are unnecessarily high, and which can already do them harm.
Let's face it, most aquarists don't really know how much nutrients to add to their planted aquarium and whether it makes sense to add anything at all.
There is a lot of "guaranteed" information on the internet about recommended aquarium plant fertilization, but I have been unable to find virtually any reliable source of information
that can explain to aquarists how much nutrients our aquarium plants really need to grow well. Therefore, I have decided to "contribute my bit to the mill" and conduct one growth experiment
to find out at what nutrient concentrations our selected aquarium plant species will grow best, what nutrient concentrations are already insufficient for them,
and what concentrations are unnecessarily high or downright inhibitory (toxic) for them. At the end of the article you will find a more extensive commentary in the form of an evaluation of the tests performed.
This was a very (time and money) demanding experiment. I decided to investigate the growth of a total of seven aquarium plants (of different demands types),
which could give us a fairly good idea of the nutrient requirements of different plant species.
Experiment objective
To create a growth curve of selected aquarium plant species depending on various external concentration of nutrients under conditions approaching the parameters of the so-called "hi-tech" planted tanks
(i.e. tanks with relatively strong lighting and heavy CO2 supply), from which one might infer the amount of nutrients needed to achieve:
1) a minimal growth → minimum concentration required for the survival of plants
2) a good growth → optimal concentrations of nutrients providing the most effective results
3) a maximum growth → minimum concentration required to achieve maximum speed or "saturation" of photosynthesis
Acknowledgements
This experiment would not have been possible without the contribution of the following people:
Prof. RNDr. Hana Čížková CSc., Jiří Novotný, Josef Levý, Jan Jabůrek, Lukáš Maňoušek, Marek Petr (akvarijni-hnojivo.cz), Martin Mithofer and Roman Souček (ProfiPlants.cz)
Dušan Zervan, Anton Fuchs, Jakub Vojtko, Martin Štyrák
Perran Trevan
Siang Kong Ting
Methods and data
Experiment diagram:
Experiment design:
In the experiment I will use five equally sized aquariums with the following dimensions: [w]8 x [l]8 x [h]16 inches and a gross volume of 4 gallons.
In each tank there will be an internal filter without filter media (JKA-MIF300) with a small spray bar,
heater with thermostat (Eheim Jäger 25W), a glass thermometer, three small plastic pots with an inert substrate (black quartz gravel with a grain size of 0.7 to 1.2 mm) .
The plants used in the experiment will be cultivated in 16G aquarium with nutrient-rich substrate (ADA Aqua Soil Amazonia),
strong lighting (~100 µmol PAR at the bottom), constant supply of CO2 (~30-40 ppm), and decent fertilizing into the water column (using the recommended dosage of Tropica Specialised Fertiliser).
At the begining of each test I will cut off equally long and equally large shoots of the same plant species which I'll weigh and plant
into small plastic pots in the tanks. One shoot into each pot.
The filter is used primarily for circulation of the water in the aquarium and for the dissolution of CO2 (it does not house any filter media).
Stable temperature will be maintained by the heaters at ~77°F (if necessary, i.e. outside the summer months) and continuously monitored by thermometers.
The same intensity of light will be ensured in each tank by the Bridgelux BXCD45 LED chips (6500 K, 9.2V, 9.2W, 950ℓm@1A)
with a directional reflectors attached on an aluminum heatsink → always one chip over each aquarium.
For the light from one of the aquarium to not affect the lighting conditions in neighboring aquariums each individual aquarium will be separated
from each other by a black divider (ground pad).
Irradiation values in each tank will be 100 µmol PAR at the bottom and 150-200 µmol PAR at the water surface.
The length of the photoperiod will be set to 10 hours (10 hours light + 14 hours dark) corresponding to the normal regime used in planted aquariums.
Carbon dioxide will be supplied to the tanks from a cylinder.1)
The amount of CO2 flowing into each tank will be regulated by Ideal Valve 52-1 needle valves
(thereby ensuring the same CO2 concentration in each aquarium).
The actual dissolution of CO2 in water will be ensured by a fine needle inserted into the filter intake.
When the gas goes through the fine needle, very small bubbles are created which get into the filter,
and are further dissolved in it, and expelled by the spray bar. The spray bar will also bring the water enriched with dissolved CO2 throughout the tank.
The supply of CO2 into the tanks will be on continuously (i.e. without overnight shutdown) for securing a stable CO2 concentration.
In the tanks there will be used a demineralized water → product of 5-stage reverse osmosis unit, whose output would be water with virtually zero
content of minerals and a minimum conductivity (1-3 µS/cm). This water void of all salts will then be enriched by a specific quantity of nutrients
prior to use in aquariums in order to achieve different concentrations of nutrients in each tank.
1) For the experiment I used a standard 4kg CO2 cylinder filled with carbon dioxide in a food-grade quality.
Plants
For this experiment I have chosen 7 species of aquarium plants with different preferences:*
= tolerant (eutrophic),
= intermediate (mesotrophic),
= sensitive (oligotrophic).
Light intensity in the units of µmol PAR (measured in the tank without equipment)
Apogee MQ-200 PAR meter with waterproof sensor
Substrate
Inert silica sand (1-2 mm fraction)
Nutrient solutions
After an initial test phase, when I was using a relatively high external concentration of nutrients (15, 30, 60, 90 and 120 mg/ℓ NO3 + proportional amounts of other essential nutrients) and when I found out
that the growth rate has not changed much at concentrations above 30 mg/ℓ NO3, I finally chose the following concentrations for this experiment:
In each aquarium different nutrient concentrations will be maintained (except CO2, alkalinity, total hardness, sulfates, and sodium):
Nutrient
Aquarium
Note
#1
#2
#3
#4
#5
pH
6.35—6.45
~7.5 degassed
ppm (mg/ℓ)
CO2
35—45
Na+
46.3
K+
1.25
2.5
5
10
20
Ca2+
25.0
5.6°dGH
Mg2+
9.1
NO3−
2
4
8
16
32
H2PO4−
0.2
0.4
0.8
1.6
3.2
10x less than NO3
SO42−
96.0
Cl−
0.001
0.003
0.005
0.01
0.02
HCO3−
61.5
2.8°dKH
ppb (µg/ℓ)
Fe[DTPA]
20
40
80
160
320
100x less than NO3
Mn[EDTA]
5
10
20
40
80
B
2.5
5
10
20
40
Cu[EDTA]
1
2
4
8
17
Zn[EDTA]
1
2
4
8
17
Mo
0.3
0.5
1
2
4
All values are in mg/ℓ (unless stated otherwise).
Results
Calibration test
Since I had no experience with such an experiment before, I decided to try this experiment first on a mock sample of three plants for which I chose five different nutrient concentrations (from lowest to highest).
Show calibration details …
Photodocumentation
2 ppm NO3 0.2 ppm PO4 0.02 ppm Fe 1.25 ppm K
4 ppm NO3 0.4 ppm PO4 0.04 ppm Fe 2.5 ppm K
8 ppm NO3 0.8 ppm PO4 0.08 ppm Fe 5 ppm K
16 ppm NO3 1.6 ppm PO4 0.16 ppm Fe 10 ppm K
32 ppm NO3 3.2 ppm PO4 0.32 ppm Fe 20 ppm K
2x Rotala wallichii
→ sensitive
2x Rotala rotundifolia
→ tolerant
2x Ludwigia sp. 'Red'
→ tolerant
Record of the plant growth
Note: The individual values in the graph are always the average height of two plants (shoots).
Rotala rotundifolia
Date
#1
#2
#3
#4
#5
Note
← flower pot
?
?
?
?
?
?
?
?
?
?
Fresh weight (initial)
Day 1
09/06
9.0
9.0
9.0
9.0
9.0
9.0
9.0
9.0
9.0
9.0
Height (initial)
Day 17
09/22
20.3
26.6
21.6
30.0
26.9
28.0
29.2
24.4
37.0
28.0
Height (final)
28.9
33.6
36.9
35.6
47.0
Height (increment)
1.534 g
1.616 g
1.878 g
1.801 g
2.414 g
Fresh weight (final)
Plant height is given in centimeters (cm).
Rotala wallichii
Date
#1
#2
#3
#4
#5
Note
← flower pot
?
?
?
?
?
?
?
?
?
?
Fresh weight (initial)
Day 1
09/06
8.0
8.0
8.0
8.0
8.0
8.0
8.0
8.0
8.0
8.0
Height (initial)
Day 21
09/26
17.5
11.5
23.2
17.5
21.7
19.5
34.0
18.6
25.3
12.8
Height (final)
13.0
24.7
25.2
36.6
22.1
Height (increment)
0.682 g
0.913 g
1.018 g
1.144 g
0.673 g*
Fresh weight (final)
Plant height is given in centimeters (cm).
* Note: The final fresh weight value of the Rotala wallichii in the 5th tank is distorted due to poor condition of the plants,
and is therefore not taken into account in the resulting graph.
Significantly lower sample weight (0.673 g) is probably due to severe toxicity, resulting in growth retardation.
Ludwigia sp. 'Red'
Date
#1
#2
#3
#4
#5
Note
← flower pot
?
?
?
?
?
?
?
?
?
?
Fresh weight (initial)
Day 1
09/06
8.5
8.5
8.5
8.5
8.5
8.5
8.5
8.5
8.5
8.5
Height (initial)
Day 25
09/30
25.2
20.5
34.3
32.5
30.5
37.0
28.7
35.5
26.3
28.7
Height (final)
28.7
49.8
50.5
47.2
38.0
Height (increment)
2.250 g
3.595 g
3.621 g
3.739 g
2.225 g**
Fresh weight (final)
Plant height is given in centimeters (cm).
** Note: As with Rotala wallichii the final fresh weight value of the Ludwigia sp. 'Red' in the 5th tank is distorted, and is therefore not taken into account in the resulting graph.
Significantly lower sample weight (2.225 g) is probably due to severe toxicity, resulting in growth retardation.
Observations
Iron precipitation + possible microelements toxicity
First week I added a MicroMix+ trace element mixture to the aquarium, with 4 iron chelates.
In the fifth (and in part in the fourth) aquarium, most of the iron was precipitated the next day.
That's why I started using Fe-DTPA chelate [after the second water change].
In addition, I applied the first dose of iron in a concentrated form from a syringe to the aquariums, which (as it turned out) resulted in an acute toxicity in R.wallichia and Ludwigia sp. (stunting)
in the 5th aquarium where the dose was highest. (PS: R.rotundifolia did not appear to have been affected by it.)
As a result, their growth slowed down, and data from the 5th aquarium (with the exception of R.rotundifolia) cannot therefore be considered reliable.
Special behavior of Rotala rotundifolia
Unfortunately, what significantly distorted the results of the continuous measurement of height in the Rotala rotundifolia plant was the fact that the individual stems bent down
(as if they wanted to grow into the ground), and only at the end of the second week the new shoots began to sprout upwards
(although the question is whether they would not bend down again over time).
The demanding Rotala wallichii will do well with minimum nutrients
An interesting preliminary finding for me is also the fact that Rotala wallichii has a positive gain in the first aquarium, where the nutrient concentration is the lowest
(only 2 ppm NO3). So it seems that even such a small amount of nutrients could be enough for this "demanding" plant to grow well (though slower).
At higher concentrations growth deformations were seen in this plant.
Results of the first calibration test
Test parameters:
Lighting: 100 µmol PAR at the bottom, 200 µmol PAR at the surface level
Temperature: 77-79°F
Filtration: internal filter without filter media (decent water circulation)
Sources of macro nutrients:
NaHCO3(HCO3),
KNO3(K, NO3),
KH2PO4(PO4)
Sources of micro nutrients:
Fe-DTPA (Fe),
trace elements mixture (other trace elements)
Commentary on preliminary results:
Ludwigia sp. 'Red' showed approximately the same biomass increases at concentrations of 4, 8 and 16 ppm NO3.
The initially measured increment of 2.225 g at a concentration of 32 ppm NO3 should be taken with caution as the plants in the 5th aquarium were negatively affected
by a too concentrated dose of microelements at the first dosing.
According to the direction of the graph, the correct value could be somewhere around 3.80 g (see the graph).
Rotala rotundifolia showed an increasing yield trend, suggesting that even relatively high nutrient concentrations (> 32 ppm NO3)
did not pose a problem to it.
However, the growth curve shows that concentrations above 8 ppm NO3 do not present any dramatic improvement in yield.
This type of plant also grew the fastest from all three tested species (9 cm long sprout grew to 35 cm in height in just 17 days).
Compared to other species, however, virtually all shoots (in all test aquariums) behaved strangely in that they did not grow upwards, but bent downwards,
and only at the bends formed new shoots. When the stems were forcibly straightened (lifted upwards), they were mostly 'recovered' and then continued to grow upwards
(however, some stems still tended to bend and grow down again).
To find out the exact cause of this behavior (whether it be the stronger lighting or too much space, where the individual plants had virtually nothing to lean around) would require further investigation.
Rotala wallichii showed very similar behavior to Ludwigia sp. 'Red'.
Nutrient concentrations above 16 ppm NO3 do not seem to produce any dramatic increase in yields, either.
The fact that this plant grows very well even at 4 ppm NO3 will probably surprise many aquarists, as it is generally accepted that this plant is a demanding one.
Tropica calls it "Advanced"
(i.e. light- and nutrient-demanding) and recommends using a nutritious substrate in combination with water column fertilization.
Ludwigia palustris 'Red'
Show Ludwigia details …
Photodocumentation
In the first sharp test I was expected to verify the results of the preliminary (calibration) test. So I successively tested the previous three types of aquarium plants
that I used in my first calibration test. I started with the plant Ludwigia sp. 'Red', as it was the one I have cultivated the most at the moment.
In the calibration test, I had three pots in each test aquarium, each with two shoots of one species of plant → in a yellow pot there were 2 shoots of Rotala wallichii,
in an orange pot there were 2 shoots of Rotala rotundifolia and in a white pot there were 2 shoots of Ludwigia sp . 'Red'.
However, every correct test should be done with at least three plants to avoid any non-standard behavior of some samples or to eliminate extremes.
A careful observer might have noticed at my preliminary test, where I used only two shoots of each plant, that each of the two shoots was growing at a different rate and had a different yield.
This is quite common because no two plants are exactly the same, so each plant will grow at a slightly different rate (pace).
Therefore it is a good habit to use at least three plants for each test and then make an average of the data obtained. Of course, the more plants are used for each test, the better
and the more accurate average results are achieved. My test aquariums are built only for three small pots (there could be five pots at the most, but some would be shaded by the aquarium equipment
[internal filter and heater], which must be in the aquarium, and moreover, it would be harder for the filter to get the water flow to the rear pots).
With smaller plants, it is possible to plant several shoots in each pot, thus obtaining more plants and thus more accurate averaged results.
However, it would not be very appropriate for more robust plants (such as Pogostemon erectus).
There were two 5cm shoots in each pot.
Data
Date
Tank #1
Tank #2
Tank #3
Tank #4
Tank #5
Note
← flower pot
237 µS/cm
245 µS/cm
251 µS/cm
260 µS/cm
282 µS/cm
Conductivity
Day 1
10/04
5+5
5+5
5+5
5+5
5+5
5+5
5+5
5+5
5+5
5+5
5+5
5+5
5+5
5+5
5+5
Height (initial)
0.420 g
0.299 g
0.414 g
0.359 g
0.329 g
0.420 g
0.373 g
0.349 g
0.385 g
0.342 g
0.407 g
0.337 g
0.343 g
0.415 g
0.357 g
Fresh weight (initial)
Day 29
11/01
26.2 20.6
14.4 13.7
19.8 19.5
14.8 17.4
25.5 20.5
17.4 28.5
30.5 22.3
29.7 20.5
29.7 31.0
26.0 26.0
26.1 27.5
26.2 33.5
28.5 28.3
35.2 27.3
30.3 27.0
Height (final)
84.2
94.1
133.7
135.3
146.6
Height (increment)
1.193 g 0.800 g
0.495 g 0.322 g
1.456 g 1.165 g
0.534 g 0.882 g
1.251 g 0.600 g
1.766 g 1.304 g
2.348 g 0.923 g
2.027 g 0.489 g
1.526 g 2.433 g
1.857 g 1.532 g
1.300 g 1.421 g
2.849 g 1.401 g
2.102 g 1.387 g
3.527 g 1.100 g
2.569 g 1.389 g
Fresh weight (final)
1.573 g
0.518 g
2.207 g
1.057 g
1.522 g
2.650 g
2.898 g
2.167 g
3.574 g
3.047 g
2.314 g
3.913 g
3.146 g
4.212 g
3.601 g
Difference
4.298 g
5.229 g
8.639 g
9.274 g
10.959 g
∑
10/25
246 µS/cm
250 µS/cm
254 µS/cm
273 µS/cm
296 µS/cm
Conduct. (Day 1)
11/01
232 µS/cm
238 µS/cm
245 µS/cm
254 µS/cm
284 µS/cm
Conduct. (Day 7)
14
12
9
19
12
Conduct. (difference)
Plant height is given in centimeters (cm).
Growth curve → yield vs. nutrient concentration
This is how the growth curve looks like, when we enter the sum of total biomass in each tank (i.e. the weight of all the plants together) into the chart.
Yield (grams of fresh weight)
Ludwigia palustris 'Red'
Concentration of NO3 (mg/ℓ)
Enter the concentration of nutrients, and find out the growth rate:
mg/ℓ NO3-
Yield: g
Growth rate: %
If we take the highest yield at a concentration of 32 mg/ℓ NO3- as the theoretical maximum (Vmax = g) calculated from the above equation,
then half yield (Km = g) should be reached at an external concentration of only mg/ℓ NO3-.
Recap:
100% yield ( g) at 32.0 mg/ℓ NO3- ← Vmax
75% yield ( g) at mg/ℓ NO3- ← optimum
50% yield ( g) at mg/ℓ NO3- ← Km
Rotala rotundifolia
Show R.rotundifolia details …
Photodocumentation
Data
Date
Tank #1
Tank #2
Tank #3
Tank #4
Tank #5
Note
← flower pot
237 µS/cm
247 µS/cm
251 µS/cm
259 µS/cm
288 µS/cm
Conductivity
Day 1
11/15
5+5
5+5
5+5
5+5
5+5
5+5
5+5
5+5
5+5
5+5
5+5
5+5
5+5
5+5
5+5
Height (initial)
0.098 g 0.084 g
0.131 g 0.124 g
0.052 g 0.075 g
0.106 g 0.095 g
0.048 g 0.101 g
0.084 g 0.059 g
0.044 g 0.155 g
0.079 g 0.105 g
0.060 g 0.063 g
0.097 g 0.059 g
0.121 g 0.071 g
0.090 g 0.109 g
0.084 g 0.065 g
0.044 g 0.081 g
0.109 g 0.160 g
Fresh weight (initial)
Day 23
12/08
13.0 18.4
15.1 9.6
15.5 15.6
15.5 22.5
14.6 13.5
22.5 15.3
27.3 18.4
7.8 10.3
20.5 21.2
19.2 15.9
15.1 10.8
27.1 17.8
37.7 19.0
34.9 22.7
22.3 14.2
Height (final)
57.2
73.9
75.5
75.9
120.8
Height (increment)
0.364 g 0.549 g
0.464 g 0.278 g
0.465 g 0.401 g
0.473 g 0.715 g
0.412 g 0.390 g
0.625 g 0.425 g
1.061 g 0.784 g
0.212 g 0.347 g
0.779 g 0.745 g
0.656 g 0.610 g
0.381 g 0.295 g
1.194 g 0.699 g
0.858 g 0.541 g
1.348 g 0.726 g
1.459 g 1.005 g
Fresh weight (final)
0.731 g
0.487 g
0.739 g
0.987 g
0.653 g
0.907 g
1.646 g
0.375 g
1.401 g
1.110 g
0.484 g
1.694 g
1.250 g
1.949 g
2.195 g
Difference
1.957 g
2.547 g
3.422 g
3.288 g
5.394 g
∑
#1
11/27
248 µS/cm
253 µS/cm
259 µS/cm
268 µS/cm
291 µS/cm
Conduct. (Day 1)
#7
12/03
240 µS/cm
246 µS/cm
251 µS/cm
262 µS/cm
287 µS/cm
Conduct. (Day 7)
8
7
8
6
4
Conduct. (difference)
Plant height is given in centimeters (cm).
Since I have 5 aquariums, 3 flower pots in each, and in each pot I have 2 plants, I had to cultivate 30 pieces of the same-size shoots,
which I cut to 5 cm in height, and then weighed them all after careful wiping.
It's really challenging work. For the plants to not dry out during weighing, I give them to plastic ZIP bags immediately after wiping.
Growth curve → yield vs. nutrient concentration
This is how the growth curve looks like, when we enter the sum of total biomass in each tank (i.e. the weight of all the plants together) into the chart.
Yield (grams of fresh weight)
Rotala rotundifolia
Concentration of NO3 (mg/ℓ)
Enter the concentration of nutrients, and find out the growth rate:
mg/ℓ NO3-
Yield: g
Growth rate: %
If we take the highest yield at a concentration of 32 mg/ℓ NO3- as the theoretical maximum (Vmax = g) calculated from the above equation,
then half yield (Km = g) should be reached at an external concentration of only mg/ℓ NO3-.
Recap:
100% yield ( g) at 32.0 mg/ℓ NO3- ← Vmax
75% yield ( g) at mg/ℓ NO3- ← optimum
50% yield ( g) at mg/ℓ NO3- ← Km
Rotala macrandra 'Narrow Leaf'
Show R.macrandra details …
Photodocumentation
Data
Date
Tank #1
Tank #2
Tank #3
Tank #4
Tank #5
Note
← flower pot
248 µS/cm
256 µS/cm
259 µS/cm
269 µS/cm
293 µS/cm
Conductivity
Day 1
02/07
5+5
5+5
5+5
5+5
5+5
5+5
5+5
5+5
5+5
5+5
5+5
5+5
5+5
5+5
5+5
Height (initial)
Ø 0.09 g
Fresh weight (initial)
Day 21
02/27
18.1 13.2
10.0 6.3
27.4 20.7
28.0 24.5
18.5 13.7
39.5 33.8
30.1 17.1
21.3 22.2
25.6 18.5
34.9 17.5
28.8 23.8
32.0 8.0
31.4 24.1
32.2 28.6
31.0 21.8
Height (final)
95.7
116.9
134.8
145.0
169.1
Height (increment)
0.831 g
0.381 g
1.181 g
1.430 g
0.683 g
1.948 g
1.483 g
1.081 g
1.497 g
1.745 g
1.359 g
1.682 g
1.943 g
1.683 g
1.732 g
Fresh weight (final)
0.741 g
0.291 g
1.091 g
1.340 g
0.593 g
1.858 g
1.393 g
0.991 g
1.407 g
1.655 g
1.269 g
1.592 g
1.853 g
1.593 g
1.642 g
Difference
2.123 g
3.791 g
3.791 g
4.516 g
5.088 g
∑
Plant height is given in centimeters (cm).
Growth curve → yield vs. nutrient concentration
This is how the growth curve looks like, when we enter the sum of total biomass in each tank (i.e. the weight of all the plants together) into the chart.
Yield (grams of fresh weight)
Rotala macrandra 'Narrow Leaf'
Concentration of NO3 (mg/ℓ)
Enter the concentration of nutrients, and find out the growth rate:
mg/ℓ NO3-
Yield: g
Growth rate: %
If we take the highest yield at a concentration of 32 mg/ℓ NO3- as the theoretical maximum (Vmax = g) calculated from the above equation,
then half yield (Km = g) should be reached at an external concentration of only mg/ℓ NO3-.
Recap:
100% yield ( g) at 32.0 mg/ℓ NO3- ← Vmax
75% yield ( g) at mg/ℓ NO3- ← optimum
50% yield ( g) at mg/ℓ NO3- ← Km
Didiplis diandra
Show Didiplis details …
Photodocumentation
Didiplis diandra in cultivation tank: 23th day after planting in-vitro plants
Data
Date
Tank #1
Tank #2
Tank #3
Tank #4
Tank #5
Note
← flower pot
Day 1
03/06
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
Height (initial)
Ø 0.05 g
Fresh weight (initial)
Day 29
04/03
14.5
8.0
21.3
20.0
13.3
26.5
24.3
13.9
29.0
23.0
14.3
25.2
25.0
14.0
25.6
Height (final)
29.8
44.8
52.2
47.5
49.6
Height (increment)
0.690 g
0.652 g
1.135 g
0.868 g
0.855 g
1.717 g
1.097 g
0.731 g
1.433 g
0.896 g
0.586 g
1.094 g
1.337 g
0.470 g
1.260 g
Fresh weight (final)
0.640 g
0.602 g
1.085 g
0.818 g
0.805 g
1.667 g
1.047 g
0.681 g
1.383 g
0.846 g
0.536 g
1.044 g
1.287 g
0.420 g
1.210 g
Difference
2.327 g
3.290 g
3.111 g
2.426 g
2.917 g
∑
Growth curve → yield vs. nutrient concentration
This is how the growth curve looks like, when we enter the sum of total biomass in each tank (i.e. the weight of all the plants together) into the chart.
Yield (grams of fresh weight)
Ludwigia palustris 'Red'
UNSUITABLE NUTRIENT SOLUTION
Concentration of NO3 (mg/ℓ)
Brief commentary (2025)
The most likely cause of failure of this test appears to be the toxicity of certain microelements (especially at higher concentrations).
Soft-water, oligotrophic species appear to be very sensitive to elevated concentrations of certain nutrients (especially microelements).
Pogostemon deccanensis (fka P.erectus)
Lab analysis
Show Pogostemon details …
Photodocumentation
Data
Date
Tank #1
Tank #2
Tank #3
Tank #4
Tank #5
Note
← flower pot
Day 1
04/10
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
Height (initial)
0.904
1.329
1.573
1.339
1.714
1.254
1.246
1.738
1.222
1.228
1.217
1.025
0.915
1.130
1.344
Fresh weight (initial)
Day 28
05/07
22.0
22.0
20.0
26.7
23.0
26.0
27.0
23.5
25.5
25.5
27.5
28.5
27.5
26.0
26.5
Height (final)
18.0
18.0
16.0
22.7
19.0
22.0
23.0
19.5
21.5
21.5
23.5
24.5
23.5
22.0
22.5
Height (increment)
7.866 g
9.505 g
9.138 g
11.392 g
12.363 g
12.867 g
13.370 g
15.969 g
14.902 g
13.350 g
16.125 g
16.745 g
13.500 g
14.909 g
15.851 g
Fresh weight (final)
6.962 g
8.176 g
7.565 g
10.053 g
10.649 g
11.613 g
12.124 g
14.231 g
13.680 g
12.122 g
14.908 g
15.720 g
12.585 g
13.779 g
14.507 g
Difference
22.703 g
32.315 g
40.035 g
42.750 g
40.871 g
∑
Growth curve → yield vs. nutrient concentration
This is how the growth curve looks like, when we enter the sum of total biomass in each tank (i.e. the weight of all the plants together) into the chart.
Yield (grams of fresh weight)
Pogostemon deccanensis
Concentration of NO3 (mg/ℓ)
Enter the concentration of nutrients, and find out the growth rate:
mg/ℓ NO3-
Yield: g
Growth rate: %
If we take the highest yield at a concentration of mg/ℓ NO3- as the theoretical maximum (Vmax = g) calculated from the above equation,
then half yield (Km = g) should be reached at an external concentration of only mg/ℓ NO3-.
Pre-cultivation → in-vitro plants from three pots in an area of about 30 × 30 cm
Live test
Details
Detail of plants from individual aquariums (day 10)
Detail of plants from individual aquariums (day 18)
Data
Date
Tank #1
Tank #2
Tank #3
Tank #4
Tank #5
Note
← flower pot
µS/cm
µS/cm
µS/cm
µS/cm
µS/cm
Conductivity
Day 1
12/16
6+6
6+6
6+6
6+6
6+6
6+6
6+6
6+6
6+6
6+6
6+6
6+6
6+6
6+6
6+6
Height (initial)
0.059 g 0.030 g
0.052 g 0.092 g
0.087 g 0.066 g
0.036 g 0.048 g
0.160 g 0.091 g
0.055 g 0.055 g
0.067 g 0.067 g
0.067 g 0.029 g
0.044 g 0.050 g
0.074 g 0.052 g
0.069 g 0.069 g
0.040 g 0.047 g
0.043 g 0.075 g
0.080 g 0.104 g
0.079 g 0.065 g
Fresh weight (initial)
Day 18
01/03
17.6 17.8
14.9 13.5
21.8 15.4
26.5 22.5
21.5 14.5
29.5 19.0
28.0 19.5
18.6 18.5
19.4 16.0
24.7 17.8
22.6 20.2
24.1 17.8
23.2 20.8
26.0 22.7
26.6 24.7
Height (final)
101.0
133.5
120.0
127.2
144.0
Height (increment)
0.531 g
0.479 g
0.720 g
0.757 g
0.697 g
0.824 g
0.763 g
0.644 g
0.685 g
0.606 g
0.635 g
0.685 g
0.732 g
0.990 g
0.937 g
Fresh weight (final)
0.442 g
0.335 g
0.567 g
0.673 g
0.446 g
0.714 g
0.629 g
0.548 g
0.591 g
0.480 g
0.497 g
0.598 g
0.614 g
0.806 g
0.793 g
Difference
1.344 g
1.833 g
1.768 g
1.575 g
2.213 g
∑
Growth curve → yield vs. nutrient concentration
This is how the growth curve looks like, when we enter the sum of total biomass in each tank (i.e. the weight of all the plants together) into the chart.
Yield (grams of fresh weight)
Rotala wallichii
UNSUITABLE NUTRIENT SOLUTION
Concentration of NO3 (mg/ℓ)
Brief commentary
The low reliability of the model is due to growth inhibition in most of the tanks, which biased the results.
Approximately 10 days after the start of the test, the plants started to deform their growth apices (see the picture above "Detail of plants ... day 10"),
which resulted in a slowing down or even stopping of growth (first in aquarium 5, and then in aquariums 4, 3, [2]).
Meanwhile, the plants in the first and second aquarium had short cells (internodes) with a large number of long leaves,
the plants in the other aquariums had long cells with a small number of short (poorly developed) leaves and their growth apices were deformed
(probably because of this, the stem also branched more often, but these lateral branches also suffered from the same defects and deformities).
For this reason, I decided to repeat the test (with the same parameters) to verify the validity of the results.
Note as of 2025:
The most likely cause of failure of this test appears to be the toxicity of certain microelements (especially at higher concentrations).
Soft-water, oligotrophic species appear to be very sensitive to elevated concentrations of certain nutrients (especially microelements).
Rotala wallichii [repetition]
Show R.wallichii2 details …
Photodocumentation
Data
Date
Tank #1
Tank #2
Tank #3
Tank #4
Tank #5
Note
← flower pot
Day 1
03/06
6+6
6+6
6+6
6+6
6+6
6+6
6+6
6+6
6+6
6+6
6+6
6+6
6+6
6+6
6+6
Height (initial)
Ø 0.065 g
Fresh weight (initial)
Day 29
04/03
24.0 24.0
21.8 21.5
32.2 33.5
31.1 27.9
24.0 20.3
31.5 26.0
29.5 20.0
31.7 28.9
30.5 26.1
34.8 20.5
27.8 23.5
33.0 33.0
28.7 21.0
28.0 27.2
30.7 21.0
Height (final)
157.0
160.8
166.7
172.6
156.6
Height (increment)
0.592 g
0.576 g
0.975 g
0.753 g
0.548 g
0.773 g
0.475 g
0.718 g
0.764 g
0.763 g
0.633 g
1.051 g
0.659 g
0.761 g
0.474 g
Fresh weight (final)
0.527 g
0.511 g
0.910 g
0.688 g
0.483 g
0.708 g
0.410 g
0.653 g
0.699 g
0.698 g
0.568 g
0.986 g
0.594 g
0.696 g
0.409 g
Difference
1.948 g
1.879 g
1.762 g
2.252 g
1.699 g
∑
Growth curve → yield vs. nutrient concentration
This is how the growth curve looks like, when we enter the sum of total biomass in each tank (i.e. the weight of all the plants together) into the chart.
Yield (grams of fresh weight)
Rotala wallichii #2
UNSUITABLE NUTRIENT SOLUTION
Concentration of NO3 (mg/ℓ)
Brief commentary
Rotala wallichii showed signs of acute toxicity in all aquaria (except the first), the causes of which cannot yet be reliably identified without further investigation.
Given that the plant grew without any negative symptoms in the culture aquarium at similarly high nutrient concentrations as in test aquaria 4 to 5, a possible explanation is that some protective factor
(e.g. higher dissolved organic matter or fulvic acids) is most likely to be operating in the culture aquarium, which is not (or only minimally) present in the test aquaria.
Note as of 2025:
The most likely cause of failure of this test appears to be the toxicity of certain microelements (especially at higher concentrations).
Soft-water, oligotrophic species appear to be very sensitive to elevated concentrations of certain nutrients (especially microelements).
Rotala macrandra
Show R.macrandra details …
Photodocumentation
Data
Date
Tank #1
Tank #2
Tank #3
Tank #4
Tank #5
Note
← flower pot
242 µS/cm
248 µS/cm
258 µS/cm
269 µS/cm
294 µS/cm
Conductivity
Day 1
05/08
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
Height (initial)
Ø 0.08 g
Fresh weight (initial)
Day 26
06/02
23.6
16.7
15.8
27.1
9.0
27.2
34.0
35.2
30.5
27.2
35.9
32.2
28.8
27.2
11.6
Height (final)
38.1
45.3
81.7
77.3
49.6
Height (increment)
1.643 g
1.236 g
0.904 g
1.946 g
0.836 g
1.781 g
1.691 g
2.294 g
2.248 g
2.261 g
2.167 g
1.715 g
1.593 g
1.751 g
0.957 g
Fresh weight (final)
1.563 g
1.156 g
0.824 g
1.866 g
0.756 g
1.701 g
1.611 g
2.214 g
2.168 g
2.181 g
2.087 g
1.635 g
1.513 g
1.671 g
0.877 g
Difference
1.563 g
1.156 g
1.360 g
1.866 g
1.784 g
1.701 g
1.611 g
2.214 g
2.168 g
2.181 g
2.087 g
1.635 g
1.513 g
1.671 g
1.592 g
Difference (adjusted Ø)
4.079 g
5.351 g
5.993 g
5.903 g
4.776 g
∑
Plant height is given in centimeters (cm).
The red values (yellow pot in aquarium #1, white pot in aquarium #2, yellow pot in aquarium #5) are the average of the remaining two values from the given aquarium, because the original values are distorted by deformed growth.
Growth curve → yield vs. nutrient concentration
This is how the growth curve looks like, when we enter the sum of total biomass in each tank (i.e. the weight of all the plants together) into the chart.
Yield (grams of fresh weight)
Rotala macrandra
Concentration of NO3 (mg/ℓ)
Enter the concentration of nutrients, and find out the growth rate:
mg/ℓ NO3-
Yield: g
Growth rate: %
If we take the highest yield at a concentration of mg/ℓ NO3- as the theoretical maximum (Vmax = g) calculated from the above equation,
then half yield (Km = g) should be reached at an external concentration of only mg/ℓ NO3-.
Recap:
100% yield ( g) at mg/ℓ NO3- ← Vmax
75% yield ( g) at mg/ℓ NO3- ← optimum
50% yield ( g) at mg/ℓ NO3- ← Km
Commentary as of 2025
This is one of my most important and most extensive experiments so far, even though at the time I mistakenly believed that the recipe I chose for this experiment
was universally suitable for all types of aquarium plants.
However, as I now know, there are at least two basic ecotypes of plants → soft-water (oligotrophic) vs. hard-water (eutrophic) species, each requiring a different approach
(i.e., not only in terms of absolute amounts and relative proportions of nutrients, but [and this seems even more important] also in terms of pH and bicarbonate content …
not to mention other potential factors that we may still know nothing about or pay no attention to).
The fact that the recipe used in this experiment is not universally suitable can be seen in two plants in particular:
Didiplis diandra and Rotala wallichii.
For these plants, the recipe used was so unsuitable that they grew poorly in all test aquaria.
I now know that these plants prefer a more acidic pH (i.e. pH < 6) without bicarbonates (i.e. KH=0).
I hope that one day I will be able to repeat this experiment under more suitable physico-chemical conditions, once I find out what they are.
The attempt to find these suitable physico-chemical parameters is a quest I have embarked on ever since.
Prof. RNDr. Hana Čížková CSc., Jiří Novotný, Josef Levý, Jan Jabůrek, Lukáš Maňoušek, Marek Petr (akvarijni-hnojivo.cz), Martin Mithofer and Roman Souček (ProfiPlants.cz)
Dušan Zervan, Anton Fuchs, Jakub Vojtko, Martin Štyrák
Perran TrevanSiang Kong Ting
= tolerant (eutrophic),
= intermediate (mesotrophic),
= sensitive (oligotrophic).
