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Experiment #7

Hard-water vs soft-water ecotypes

Combating increased cation demands and microelement toxicity

Main objective

Identify the optimal parameters for cultivation of aquarium plants.

Plants

In this experiment I decided to use the following plants, which seem to be good representatives of different ecotype groups:

Hard-water species

Hygrophila corymbosa
  • Hard-water, eutrophic species
    • bicarbonate (HCO3) tolerant
    • phosphate (PO4) tolerant
    • organic substrate tolerant
    • µ tolerant
Alternanthera reineckii 'Mini'
  • Intermediate, mesotrophic species (?)
    • bicarbonate (HCO3) sensitive
    • phosphate (PO4) sensitive
    • organic substrate sensitive
    • <unknown µ sensitivity> ← needs further testing

Soft-water species

Ammannia pedicellata 'Gold'
  • Soft-water, oligotrophic species
    • bicarbonate (HCO3) sensitive
    • phosphate (PO4) sensitive
    • organic substrate sensitive
    • efficient nutrient uptaker
      • µ hyper-accumulator with poor regulatory ability
      • µ ultra-sensitive
Rotala wallichii
  • Soft-water, oligotrophic species
    • bicarbonate (HCO3) sensitive
    • phosphate (PO4) sensitive
    • organic substrate sensitive
    • efficient nutrient uptaker (+ ultra-efficient µ uptaker)
      • µ hyper-accumulator with poor regulatory ability
      • µ sensitive
    • undemanding CO2 user ← can cope with naturally low CO2 levels

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

  • In aquariums 2 and 5, approximately 2.5 cm (1") of organic substrate for aquatic plants [from a gardening store] was used, covered with a layer of fine silica sand (1-2 mm fraction).
  • In aquariums 1, 3, 4, and 6, there was no substrate.

Nutrient solutions

In this experiment, I am going to test the following six recipes in a low pH/KH environment:

PS: By clicking on the tank number or recipe name, you can view the corresponding recipe in the nutrient calculator.
TankRecipepHCO2K+Ca2+Mg2+NH4+NO3−H2PO4−SO42−Cl2−HCO3−FeMnBZnCuMo
#1
hard
5ppm
(mg/ℓ)		1015207030.39210ppb
(µg/ℓ)		201043.61.20.002
#2
[P+µ]
Organic substrate0000000
#3
N+P
0.54.60.7
#4
soft
5ppm
(mg/ℓ)		10231030.3120.20ppb
(µg/ℓ)		201043.61.20.002
#5
[P+µ]
Organic substrate0000000
#6
N+P
0.54.60.7
If no value is listed for a specific nutrient in any of the columns, it means that the concentration of that nutrient is the same as in the main tank (i.e., tank #1 for hard-water species, or tank #4 for soft-water spp.). Half of the water is changed every week (usually on Saturdays). The above values represent the nutrient concentrations in the newly replenished water (except CO2, which is a continuously [24/7] maintained concentration). All nutrients are added to the water once a week (macronutrients are dosed at water change, micronutrients on Monday).

Hard-water ecotypes

hard
recipe designed for species with higher cation demands
[P+μ]
organic substrate (no P+µ in water)
N+P
increased concentration of N+P

Soft-water ecotypes

soft
recipe designed for oligotrophic species
[P+μ]
organic substrate (no P+µ in water)
N+P
increased concentration of N+P

Notes

Note on pH

  • I'll try to keep the pH about the same everywhere (around 5).
  • To achieve this, I will not use any bicarbonates (HCO3−) in the recipes, so there will be virtually zero alkalinity (KH = 0). This way the initial pH should be around 5.5. With the addition of 10 ppm CO2, it should drop to 5.
  • For pH control I will use either bicarbonates (to increase pH) or hydroxides (to decrease pH).

Note on the unsuitability of using flowering plants → The Alternanthera case

Why not use flowering plants in experiments

One of the plants I used in this experiment was Alternanthera reineckii ‘Mini’, which [unfortunately] was in bloom at the time. As it turned out, using flowering plants was not a good idea. Why?

Flowering plants redirect energy to reproduction—developing flowers, seeds, etc. This means less resources for growth and adaptation. When submerged, plants need to adjust morphologically and physiologically, like growing submerged-type leaves. Flowering plants might lack the energy for this, causing delays. The presence of apical flowers halts terminal growth. In some plants the tip is occupied by a flower, so the main stem can't grow new leaves. Instead, they have to rely on axillary buds at internodes, which takes more time and energy to activate. Flowering also involves hormones like gibberellins and auxins focused on reproduction, which might suppress growth-promoting hormones needed for new leaf development. Submergence stress adds ethylene buildup, further complicating things for flowering plants.

This problem affected A. reineckii to such an extent that it made no sense to continue with it in the experiment, because even if it had eventually succeeded in transitioning from the emersed to the submerged form, the differences in growth (and the survival rate of individual leaves) between the individual aquariums were so significant that it would not be possible to determine what was due to the recipe used and what was due to the difficulties of this demanding transition. In addition, these plants (or rather their old dying leaves) have become a significant source of algae.

Algae infestation
Alternanthera

Therefore, I decided to remove this plant species from the experiment.

Documentation

Carbon Dioxide (CO2)

Tank#1#2#3#4#5#6
Concentration121111n/a1012
All values are in ppm (mg/ℓ)

Week #1 (day #6)

#1
pH 4.3
#2
pH 6.1
#3
pH 4.3
#4
pH 4.3
#5
pH 6.1
#6
pH 4.3
  • All plants arrived in excellent condition, except for Alternanthera

Week #2-4

#1
pH 4.3
#2
pH 6.1
#3
pH 4.3
↖ Week #3 (day 20)
#1
pH 4.3
#2
pH 6.1
#3
pH 4.3
↖ Week #4 (day 25)
#4
pH 4.3
#5
pH 6.1
#6
pH 4.3
↖ Week #2 (day 12)
↖ Week #3 (day 18): Before trimming & replanting
#4
pH 4.3
#5
pH 6.1
#6
pH 4.3
↖ Week #3 (day 20): After trimming & replanting

Week #5 (day #32)

#4
pH 4.3
#5
pH 6.1
#6
pH 4.3

Details  

Hygrophila in aquarium #1

  • Subjectively in the best condition, beautifully straight leaves, nice/rich coloration
  • The most vigorous root system with a series of long, fine hairs pointing straight up
#1
#1
#1

Hygrophila in aquarium #2

  • Similar condition as in aquarium #1, but some leaves are slightly deformed or wavy
  • The coloration of the leaves seems to be less rich (paler) here
#2
#2

Hygrophila in aquarium #3

  • The largest biomass, but also the most deformed leaves (wavy, twisted)
  • Interestingly, the root system here lacks the fine, long hairs pointing straight up
#3
#3
#3

Ammannia & Rotala in aquarium #4

  • The growth tips of Ammannia and Rotala are slightly deformed (stunted)
  • The root system of Ammannia and Rotala is very poor
  • The lower leaves of Ammannia often turn brown (interestingly, it is usually the left (or right) half of the leaf that turns brown first, while the other half remains normal) and tend to be greener
  • Rotala growth tips appear paler (more pinkish)
#4
#4
#4
#4
#4
#4
#4
#4
#4

Rotala's trimming & replanting

#4
#4
#4

Ammannia & Rotala in aquarium #5

  • The growth tips of Ammannia and Rotala are slightly deformed (stunted)
  • The root system of Ammannia and Rotala is very poor
  • The lower leaves of Ammannia often turn brown (interestingly, it is usually the left (or right) half of the leaf that turns brown first, while the other half remains normal) and tend to be greener
  • Rotala growth tips appear paler (more pinkish)
#5
#5
#5
stunting
#5
turning glassy & disintegrating
#5
#5
#5
#5

Ammannia & Rotala in aquarium #6

  • Compared to aquarium #4, there are not many differences, but there is clearly more algae
  • Overall, however, the plants here are in slightly worse condition (compared to aquarium #4) and appear to be somewhat smaller (especially in the case of Rotala)
#6
#6
#6
#6
#6
#6
#6
#6

Results

Subjective assessment

The following data is a brief description of the visual condition of the plants in each aquarium (1 to 6). Green indicates best condition, blue indicates good condition and red indicates fair condition.

In the first set (tanks 1-3), there was only Hygrophila:

Hygrophila corymbosa

  • 7.1 → pH 4.3 = best shape, straight leaves, nice/rich coloration
  • 7.2 → pH 5.8 = good shape initially, but some leaves slightly deformed/wavy, paler coloration
  • 7.3 → pH 4.2 = good shape, largest biomass, but also the most deformed leaves of the three

In the second set (tanks 4-6), there were Ammannia and Rotala:

Ammannia pedicellata 'Gold'

  • 7.4 → pH 4.5 = good shape initially, later slightly deformed (stunted) growth tips
  • 7.5 → pH 6.1 = bad shape, disintegrating
  • 7.6 → pH 4.3 = good shape initially, later slightly deformed (stunted) growth tips

Rotala wallichii

  • 7.4 → pH 4.5 = good shape initially, later slightly deformed (stunted) growth tips
  • 7.5 → pH 6.1 = bad shape at the end, severely stunted growth tips
  • 7.6 → pH 4.3 = good shape initially, later moderately deformed (stunted) growth tips

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.

Hygrophila corymbosa

15-20-7 mg/ℓ K:Ca:Mg, 3-0.3 mg/ℓ NO3:PO4, 20 µg/ℓ Fe
  • Tank 7.2: organic substrate (no P+µ in water)
  • Tank 7.3: increased concentration of N+P
% ppm
Tank C N P K Ca Mg Na Fe Mn Zn Cu Substrate
7.1 38.14 3.09 0.26 6.42 3.28 0.63 0.006 69 57 115 14.3 Substrate
7.2 37.85 2.85 0.37 6.14 3.45 0.71 0.07 75 84 84 12.7 Substrate
7.3 38.70 3.56 0.32 6.05 2.80 0.61 0.005 57 53 118 13.9 Substrate

Ammannia pedicellata 'Gold'

2-3-1 mg/ℓ K:Ca:Mg, 3-0.3 mg/ℓ NO3:PO4, 20 µg/ℓ Fe
  • Tank 7.5: organic substrate (no P+µ in water)
  • Tank 7.6: increased concentration of N+P
% ppm
Tank C N P K Ca Mg Na Fe Mn Zn Cu Substrate
7.4 41.64 3.09 0.27 2.82 1.92 0.75 0.24 50 263 66 6.5 Substrate
7.5 40.41 3.58 0.51 2.90 2.09 0.56 0.31 404 330 96 13.3 Substrate
7.6 41.84 3.49 0.35 2.98 1.74 0.71 0.24 48 166 74 8.3 Substrate

Rotala wallichii

2-3-1 mg/ℓ K:Ca:Mg, 3-0.3 mg/ℓ NO3:PO4, 20 µg/ℓ Fe
  • Tank 7.5: organic substrate (no P+µ in water)
  • Tank 7.6: increased concentration of N+P
% ppm
Tank C N P K Ca Mg Na Fe Mn Zn Cu Substrate
7.4 40.61 2.33 0.22 3.96 1.56 0.53 0.31 38 51 29 7.9 Substrate
7.5 40.58 2.94 0.64 3.50 1.38 0.52 0.76 234 105 52 8.1 Substrate
7.6 40.95 2.79 0.36 3.53 1.44 0.52 0.25 41 50 36 11.8 Substrate

My commentary & interpretation

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