Ecology of the planted tank

and as a solid foundation
for a good
which we put to test
in the fire of factual
Published: 2013-10-29, Updated: 2016-04-27

Experiments: Algae and dissolved organic matter (DOM)

Algal blooms are related to the amount of organic matter – true or false?


"Large amount of „total organic carbon“ (TOC) causes algal proliferation."

Algae and dissolved organic matter

"Most people do not realize that aquatic plants release a large amount of photosynthate products into the water. People believe that the flow of chemicals is only one-way. But aquatic plants interact with their environment. Sugars and other carbohydrates as well as the nutrients that are released from the plants serve as food to the bacteria, which in turn serve the plants – for example, they transform minerals (salts) into plant-usable forms. Plants, therefore, in a sense, care for their own zoological garden. In nature, these products have a very low concentration, mainly due to the huge mass of water, but in our aquariums (which are really tiny compared to ponds or lakes), the released products of photosynthesis (i.e. photosynthates) easily accumulate and "clutter" the surface of the plants. The accumulated material then acts as a barrier that prevents the effective absorption of nutrients and CO2, but when these organic products start to decompose they attract algae and encourage their growth, Therefore, it is also unreasonable to dose large amounts of nutrients while neglecting maintenance. High doses of nutrients require high level of maintenance, and less frequent maintenance requires small amounts of nutrients. Therefore, when someone says he doesn't like frequent water changes, we have to answer him that he need to reduce fertilizer dosage. And if we want to reduce the amount of nutrients without asking for trouble, we also need to reduce the lighting. These three factors are closely linked, and if people do not understand it, they get into trouble. Therefore, as long as the aquarists keep the tank clean, they can safely dose virtually any amount of [inorganic] nutrients."

— Clive Greene, Great Britain (private correspondence)

"In general, it can be said that salts (inorganic nutrients), which we add to our aquariums in a certain amount, have very little direct impact on algae growth. The only exception is perhaps ammonia-based substances, which is also one of the main reasons why we rarely recommend the use of ammoniacal compounds as a nitrogen source in aquariums (the second reason is their toxicity). As I have found, "nutrients" that are directly related to algal overgrowth are the ones we associate with "decay". Thus, algae proliferation usually occurs due to metabolic waste (fish excrements), decomposing unused feed, dead animals, dead bacterial colonies, etc., the amount of which exceeds the ability of the system to directly utilize them or at least convert them to nitrates. Thus, with few exceptions, the common denominator of algae proliferation is high level of dissolved organic matter (DOM), low oxygen levels, and low or unstable amounts of CO2."

— Biollante, Arizona (private correspondence)

Nutrient cycle

Fish and plants (as well as feeding) are the source of organic waste (faeces, detritus, decaying leaves and dead animals). These organic substances undergo decomposition processes (decomposition or mineralization) in the aquarium, in which the decomposers (aerobic and anaerobic bacteria and fungi) convert them into inorganic substances (carbon dioxide, water and nutrients). Important steps in the decomposition process are fragmentation (decomposition of detritus into smaller particles), leaching (precipitation of water-soluble inorganic nutrients into the substrate), catabolism (bacterial and enzymatic decomposition of organic detritus into simpler inorganic substances → lactic acid, acetic acid, carbon dioxide, ammonia and urea), humification (the transformation of organic matter into humus, which is highly resistant to microbial activity and extremely slowly undergoes decomposition, and due to its colloidal nature serves as a nutrient reservoir) and mineralization (the process by which inorganic nutrients are released from the humus by the action of microorganisms). All these steps in the process of decomposition of the detritus take place simultaneously. Decomposition is a process that typically requires large amounts of oxygen. One of the resulting products of decomposition → ammonia (NH3) is then transformed by nitrifying bacteria first to nitrites (NO2), and then to nitrates (NO3). Similarly, bacteria also transform organic phosphorus compounds into inorganic orthophosphates (PO43-), which are often referred to simply as phosphates. Only these inorganic substances (nitrates and phosphates) serve as food for plants. Unlike plants, however, a number of freshwater algal species belong to so-called mixotrophic organisms. This means that algae can feed on both inorganic and organic food! Thus, while plants need bacteria to live that transform complex organic compounds to simple inorganic nutrients, algae can do without them. Thus, although algae (like plants) are phototrophic organisms [which gain energy from light through photosynthesis, and use the energy thus obtained for producing building materials for their growth (= sugars) from nutrients they get from water (CO2, nitrates, phosphates, etc.)], under certain conditions they can reorient to a heterotrophic way of life, where they are ale to gain carbon (the basic building block for the formation of their own organic matter) from organic substances produced by other organisms.

It is clear from the above that both inorganic and organic substances can play a role in algal proliferation. Some correlation between the increased dissolved organic matter (DOM) and algae proliferation has also been observed by many aquarists. It is quite possible that the increased level of dissolved organic matter may also function as a signal by which the algae "sense" that there is a good time to proliferate. Another factor that can "launch" the algal proliferation is ammonia (NH3). It is produced by decomposition processes and could, to a large extent, also act as a catalyst because it is the best digestible source of nitrogen for algae (as well as plants). However, its amount in the aquarium is usually negligible, because either nitrifying bacteria (in the substrate or in the filter) or the plants themselves can degrade (remove) it relatively quickly.

Note: Aquaristic test kits, which are used to measure the concentrations of various substances (nutrients) in water, only detect inorganic nutrients ! However, most nitrogen and phosphorus-based substances are present in the aquarium as organic compounds. organických sloučenin.

Furthermore, it is worth remembering that a large amount of organic matter in water leads to a rapid decrease in oxygen concentration in water (since in decomposition the aerobic bacteria consume a large amount of oxygen) → see the following equation for remineralizing organic material to oxidized inorganic minerals:

(C106H124O36)(NH3)16(H3PO4) + 150 O2 106 CO2 + 78 H2O + H3PO4 + 16 HNO3 + energy
organic compound (sugar) oxygen carbon dioxide water phosphate nitrate

Results of the analysis conducted by Jeffrey K. Funk, PhD.

Sample Al B Cu Fe K Mn Mo Sr Zn Ca Mg GH KNK TOC1) CO2 Algae*
CA tap water 0.03 n/a 0.04 < 3.3 < < 0.23 0.12 48   11   9.3°dGH 10°dKH 2.9 - -
CA tap.w.+subst. 0.08 n/a < 0.10 35   < 0.01 0.15 0.03 26   6.7 5.2°dGH 4.1°dKH 8.9 - -
CA rev.osmosis1 < n/a < < 1.1 < < 0.03 < 6.6 1.6 1.3°dGH 2.6°dKH 1.8 - -
CA rev.osmosis2 < <0.10 < < <2.0 < < < < <1.0 <1.0 <0.5°dGH <0.5°dKH 1.8 - -
CA Tank (2013-09-01) < n/a < 0.04 41   < < 0.25 0.41 48   12   9.5°dGH 9.9°dKH 12.1 BBA
CA Tank (2013-09-12) < n/a < 0.04 36   < < 0.17 0.27 27   7.4 5.5°dGH 5.9°dKH 9.3 BBA
CA Tank (2013-10-02) 0.06 n/a < 0.03 33   < 0.01 0.14 0.03 26   7.1 5.3°dGH 5.2°dKH 10.6 BBA
CA Tank (2013-10-18) 0.02 0.12 < 0.30 28   < < 0.09 0.09 16   4.5 8.6°dGH 4.4°dKH 11.0 BBA
CA Tank (2013-10-23) < 0.13 < 0.03 36   < < 0.09 24   5.8 4.7°dGH 13.1 → before WC
CA Tank (2013-10-23) < 0.12 < 0.14 28   < < 0.08 16   4.6 3.2°dGH 12.1 → after WC
CA Tank (2013-10-30) < 0.13 < 0.20 34   < < 0.27 22   5.3 4.3°dGH 13.0 → before WC
CA Tank (2013-10-30) < 0.10 < 0.02 26   < < 0.03 15   4.1 3.1°dGH 9.9 → after WC
CA Tank (2013-11-13) < 0.13 < 0.05 31   < < 0.03 18   4.6 3.6°dGH 10.4 → before WC
CA Tank (2013-11-22) < 0.12 < 0.13 32   < < 0.03 18   4.2 3.5°dGH 8.0 → before WC
CA Tank (2013-12-12) < 0.12 < 0.01 33   < < 0.05 20   4.2 3.8°dGH 8.9 → before WC
TG tap water 0.02 n/a 0.01 < 3.3 < < 0.27 0.19 41   11   8.4°dGH 5.9°dKH 1.7 - -
TG 20g (2013-10-12) < n/a < < 57   < 0.01 0.26 0.02 35   10   7.5°dGH 4.2°dKH 1.6 no BBA
TG 40g (2013-10-12) < n/a < 0.03 70   < 0.01 0.25 < 39   11   8.0°dGH 5.4°dKH 3.3 no BBA
RJ tap water < <0.10 0.01 0.02 2.6 < < 0.10 0.07 32   8.0 6.3°dGH 9.4°dKH 3.1 - -
RJ 75g (2013-10-14) < 0.19 0.02 1.70 66   < 0.02 0.20 0.07 52   9.9 9.6°dGH 6.9°dKH 7.6 little BBA
BM tap water 0.02 0.16 < < 7.0 < < 0.54 < 36   4.0 6.1°dGH 5.3°dKH 8.1 - -
BM (2013-10-17) 0.04 0.26 0.02 2.70 73   < 0.01 0.53 0.10 33   11   7.2°dGH 3.8°dKH 10.4 GSA,GDA,BrA
AT tap water1 0.01 n/a < < 9.7 0.32 < 0.41 0.05 29   18   8.2°dGH 2.5°dKH 1.0 - -
AT tap water2 0.02 n/a 0.01 < 2.0 < < 0.07 0.01 19   5.2 3.8°dGH 4.9°dKH 1.7 - -
AT rev.osmosis < n/a < < <1.0 < < < < 1.3 <1.0 <0.5°dGH 0.6°dKH <1.0 - -
AT 30-B (2013-09-01) 0.06 n/a 0.01 0.01 140   < < 0.51 0.01 110   32   23.0°dGH 17°dKH 7.8 ?
AT 90-P(2013-09-01) 0.02 n/a 0.05 1.60 100   < < 0.10 0.05 33   10   7.0°dGH 5.2°dKH 10.6 ?
AT 90-P (2013-09-18) 0.01 n/a 0.08 1.20 68   < < 0.21 0.04 3.6 10   7.5°dGH 5.1°dKH 12.9 ?
MT tap water1 < n/a 0.01 < 1.9 < < 0.10 < 39   9.2 7.6°dGH 9.4°dKH 1.5 - -
MT tap water2 < n/a 0.01 < <1.0 < < 0.06 < 20   7.8 4.6°dGH 7.0°dKH 1.3 - -
MT tap water3 < n/a 0.06 < 6.7 < < 0.24 0.10 59   19   13.0°dGH 11°dKH 2.5 - -
MT 90g3 (2013-10-07) < n/a 0.04 0.14 <1.0 < < 0.27 0.18 20   7.4 4.5°dGH 7.3°dKH 4.2 ?
MT 90g2 (2013-10-07) < n/a 0.26 0.01 23   0.01 < 0.06 0.03 54   19   12.0°dGH 7.7°dKH 5.6 ?
MT 180g (2013-10-07) < n/a 0.02 < <2.0 < < < < 1.9 1.3 0.6°dGH 1.2°dKH 5.1 ? many BBA
KW 12g (2013-10-20) 0.07 <0.10 < 0.03 3.7 < < 0.06 < 17   5.9 2.4°dGH 0.8°dKH 5.0 little BBA
KW 33g (2013-10-20) 0.05 <0.10 < 0.02 3.9 < < 0.07 < 16   6.5 3.7°dGH 0.9°dKH 7.8 little BBA
KW 50g (2013-10-20) 0.10 <0.10 < 0.05 2.0 < < 0.04 < 9.6 4.7 3.7°dGH 1.1°dKH 8.3 many BBA
KW 75g (2013-10-20) 0.02 <0.10 < 0.04 4.1 < < 0.07 < 16   6.8 3.7°dGH 2.4°dKH 6.6 many BBA
UDGags tap water < < 0.04 < 2.8 < < 0.01 18   29 8.8°dGH 1.2
UDGags (2014-01-13) 0.05 1.5  0.18 11    78 0.03 0.09 0.57 20   26 9.2°dGH 22.4 → before WC
1) TOC is expressed in milligrams of carbon per 1ℓ of water (ppm C)
* Algae:
BBA = black beard algae (audouinella)
GSA = green spot algae (coleochaete)
GDA = green dust algae (chlamydomonas, ankistrodesmus, chlorococcum)
BrA = brown algae (diatoms)
WC = water change

BBA = black beard algae (Audouinella genus)

Note: All results are in ppm. Metal analysis was performed on the ICP-OES device. This device measures all the carbon compounds in your water by converting them to carbon dioxide, which is then measured by an infrared sensor. Basically it has two steps. In the first step, the sample is acidified. This converts all inorganic carbon (HCO3- and CO32-) to CO2, the amount of which is measured. So this part will measure the total inorganic carbon (TIC). In the second step, an oxidizing agent is added to the sample to decompose all organic carbon to carbon dioxide, the amount of which is again measured. This part will measure the total organic carbon (TOC). TIC & TOC analysis results were analyzed by method SM 3510 C - heated-persulfate oxidation. General hardness (GH) are in units of °dGH, calculated from ppm CaCO3 eq (calculated). Please note that these samples have undergone limited quality/quality control so that analysis results are for personal use only. These results may not be used for regulatory reporting purposes or compliance testing (resulting in a Declaration of Conformity). Also, keep in mind that if someone adds a lot of fertilizer to the aquarium, such as Excel, Flourish Fe, Flourish Nitrogen, etc., which contain a large amount of organic matter, it is definitely to be expected that these products will have an impact on results of this analysis. If you would like to find out how much impact they have on your tank and the results of the analysis, you would have to remove more samples and do more testing. Another thing you should not forget is that TOC only measures organic substances in the water column. So if you have a really polluted tank with lots of animal waste products, then most of these organic substances will not dissolve in the water and will not be taken into account when analyzing the TOC. It is believed that organic residues contain some organic compounds that will be released into the water column, which may be accompanied by an increase in TOC levels in the assay.

Source: Organics Analysis, page #7

TOC & Flourish Excel

Red algae on Anubias leaf (40x magnification)

Results of laboratory analysis of Seachem Flourish Excel by Jeffrey K. Funk, PhD .:

| 0.06% solution of Excel |  9.007 ppm TOC |
|  0.1% solution of Excel | 14.397 ppm TOC |
|  0.2% solution of Excel | 27.965 ppm TOC |

By a quick and dirty calculation we could say that the difference is approximately 13.5 ppm per 0.1% Excel. Therefore, the neat Flourish Excel TOC concentration is around 13,500 ppm TOC.

At the recommended initial dosage of 5 mℓ Excel to a 40ℓ (10G) aquarium, the TOC added is 1.7 ppm TOC [13500 x 5 mℓ / (40ℓ / 1000)].

At the recommended subsequent dosage of 5 mℓ of Excel to a 200ℓ (50G) aquarium, the TOC added is 0.3 ppm TOC [13500 x 5 mℓ / (200ℓ / 1000)].

Source: Organics Analysis, page #12

Can we assume that TOC can be considered as an approximate (or not so approximate) indicator of accumulating 'organic substances' in our tanks?

"TOC is the measure of 'organic matter' in your water. The problem of organic matter generally lies in the fact that (1) there are more ways to measure 'organic substances' → as TOC (total organic carbon), COD (chemical oxygen demand), or BOD (biochemical oxygend demand), (2) for aquarists there is no simple way to measure organic pollution at home (i.e. there is no Seachem, ELOS or API test kit for analysis of organic substances), and (3) there are not too many comparative data (due to problem # 2) which suggests what TOC/COD/BOD values ​​are actually 'acceptable'. What TOC/COD/BOD values ​​are considered normal for drinking water? What TOC/COD/BOD values are considered "high" with respect to organic pollution in our tanks, and what are the "medium" or "low"? As aquarists we would love to say, "TOC/COD/BOD value exceeding the level X is already considered too high and will result in an algae proliferation (with Y likely to be a red algae)". Each of these techniques is a valid and useful measure of organic pollution, but they are not necessarily interchangeable.

COD is probably the best known method of the three (TOC, COD, BOD), but it's not an analysis I would like to do ... because the COD test is very dangerous. This test requires the use of the salts of mercury, silver, chromium, as well as concentrated sulfuric acid. The only person (I know of) who routinely "analyzes" organic pollution as COD is Amano, and to be honest, I have no idea what principle his 'ADA Pack Checker COD' works on at all. However, since the 'COD' procedure using the 'ADA Pack Checker COD' is (by far) not similar to the official method for laboratory analysis of COD, I am not even sure if it is possible to believe his results.

Therefore, the main problem with TOC analysis is the fact that we simply do not have a very large collection of data from which to draw and say (1) what is the ideal range of TOC values, and (2) what TOC value is already high or problematic. As far as I know, nobody can tell me that. Even people, who proclaim how bad organic substances are, are often not able to give a specific range of values (if anyone can let us know!). To solve this problem, we'll just have to analyze more samples and publish the results so that we can draw something useful when looking at them."

– Jeffrey K. Funk, PhD.

A new view of the substances balance in the aquarium

Author: Karel Rataj (1990)

Excessive accumulation of minerals is most often considered to be the cause of turbid water, stagnant yellowish plants overgrown with algae, and lethargic movements of fish. They are created by bacterial decomposition of fish excrements, plant remnants and food. Of these minerals, nitrates and phosphates are most important for biological processes in the aquarium.

In chemical analyzes, we found that the concentration of nitrates and phosphates in turbid, algae-infested tanks is almost zero. Conversely, the tanks, which (compared to aquariums in a downright poor state) showed up to tenfold higher concentrations of the monitored substances, had crystal clear water with nice plants.

By closer investigation, we found that intense mineralization (i.e. aerobic microbial decomposition of fish excrements to mineral substances, which must be accompanied by an increase in electrical conductivity), is rarely carried out there, and if so, it's usually only shortly after the tank is set up. Stagnation of mineralization is then closely related to negative phenomena such as algae proliferation, plant growth retardation, yellowing of plant shoots and water turbidity.

In addition to the chemical differences, it was possible to observe considerable differences in the biological variations between the variants. In the control tanks where zeolite was used, plant stagnation and intensive algal growth occurred after about 14 days. The water in the tanks was cloudy, and deposits of detritus accumulated on the sand. The plants were dwarfed and completely algae-covered at the end of the experiment. In contrast, in the tanks where Lewatit (a selective anion exchange resin that exchanges inorganic acid anions as well as anions of humic and organic substances for chloride anions) was used, the plants were lush green, completely free of algae or cyanobacteria that did not appear even on the aquarium glass. The water was crystal clear throughout the whole experiment, there was no trace of detritus on the sand. Based on the observed phenomena and measured values we come to the following conclusions:

Stagnation of plants, accompanied by intense development of algae and cyanobacteria, water turbidity and accumulation of detritus in some of our test tanks were not accompanied by an increase in electrical conductivity, and thus by no increase in nitrate concentration as well. However, oxidizable organic substances have increased intensively. Fresh plant growth and generally optimal conditions in the Lewatit tank were characterized by opposite relationships. The electrical conductivity values increased up to two times at the end of the experiment, while the oxidizability was approximately four times lower.

We explain these differences by different intensity of microbial mineralization in individual variants of tanks. Indeed, a sufficiently intense mineralization occurs only under certain optimal conditions. This includes, in particular, sufficient oxygen in water and sediment, appropriate pH and the presence of some substances (microelements, vitamins, readily degradable energy-rich organic substrates). Another limiting factor may be the presence of some inhibitory or toxic substances in water such as chlorine, pesticides, detergents and phenols.

If the above conditions are not met, and in most aquariums this is not the case, then the mineralization is inadequate or instead a fermentation occurs. Microbes in these processes gain energy by decomposing organic substances into simpler substances, but not to minerals. The compounds thus formed have inhibitory effect on both fish and plants.

Due to disrupted mineralization, plants lack nutrients, so they turn yellow and stop growth. Instead of higher plants, algae grow, which are not so sensitive to organic pollution and can thrive at lower nutrient levels, mainly of carbon and iron. In addition, weakened plants, to a much lesser extent excrete algicidal substances that have been demonstrated in healthy plants.

A large amount of oxygen binds to the increasing concentration of organic substances which continues to deteriorate the conditions for mineralization. The adverse effects of mutually reinforcing factors result in a disruption of the biological balance with all the consequences.

Undoubtedly, to eliminate these factors it is necessary to:

  1. Optimize plant growth by continuously adding the necessary nutrients in a suitable form, which will compensate the lack of mineralization.
  2. Optimize conditions for aerobic mineralization bacteria.

Problems with growing plants

Author: Karel Rataj (2000-2001)

In our experiments with plants, we concluded that the main reason why most aquariums do not look according to our liking is the lack of microbial activity. Especially those who mineralize organic waste. As a result, minerals (nitrates, carbon dioxide, etc.) are produced that serves plants as nutrients. But poor tap water quality and inappropriate filtering techniques minimize the beneficial effects of microbes. As a way out of this situation we offered so-called biological filtration. What are the other ways to speed up the "lazy" bacteria?

For further consideration, I was inspired by an article by Michael Kemp and Laura Murray in the Aquatic Botany journal. These scientists investigated the activity of mineralizing bacteria in the natural lake sediment. They found that the activity of these bacteria is several times greater in sediment that was rooted by aquatic plants (Potamogeton perfoliatus). How this phenomenon can be explained?

There is a very narrow symbiosis between plants and microbes. For plants, it is vital that microbes break down organic waste into nutrients. Otherwise, substances that are toxic to plants are produced. Roots rot and the plant stagnates. Therefore, the plant is trying to support those microbes that are useful to it. And it does so by producing a range of substances to optimize its close surroundings.

Which substances are they? First, it is oxygen. When we observe the aquarium with well-growing plants, we will see [mainly in the afternoon] thin chain of bubbles leaking from plants. It is the oxygen that plants produce in photosynthesis. The existence of these bubbles is proof that our plants grow really well. The oxygen thus produced is not released by the leaves only. With the help of the air tissues that fill most aquarium plants, the plants push the oxygen very efficiently also into the root zone, creating optimal conditions for the bacteria that urgently need it in order to mineralize organic matter.

In this context, I would like to emphasize two extremely important aspects. The above-described phenomenon (i.e. massive air tissue allowing oxygen to be transported to the root zone) is to be understood as adaptation of plants for the growth in the mud and oxygen-poor sediments. Therefore, even under such conditions, plant roots do not rot. If the roots of the plants rot and get black, it is not due to a compactness and little oxygenation of the aquarium substrate, but because the plants are missing something, thus they do not assimilate well and produce little oxygen. Decayed roots are a sign of a mistake in plant nutrition and a considerable amount of oxygen in the aquarium substrate as a whole!

In addition to oxygen, however, the plant produces a number of other substances that have a beneficial effect on the activity of useful microbes. These are different sugars, amino acids, vitamins, enzymes and other "goodies". For these reasons, a healthy plant attracts microbes and its amount on its roots and leaves is much larger than in the surrounding water. With a little exaggeration, the symbiosis of plants and microbes could be compared to a flowering tree covered with bees. The tree attracts bees with its sweet flowers and they in turn pollinate it.

Vital plants support the activity of useful bacteria that ensure that in the aquarium there does not accumulate organic waste that is toxic to both plants and fish. However, stimulated microbes, in turn, activates the plant by producing substances that the plant receives as nutrients. So in fact, by taking proper care of the plants, we are improving the conditions in the whole aquarium. Therefore, for example, a good plant fertilizer could be called "Fish fertilizer" with some exaggeration. This phenomenon is called feedback. Understanding all the consequences of the "plant – microbes – fish" bond is essential for influencing aquarium processes.

Conclusions on plant nutrition:

  1. Due to unsuitable technological procedures (poor filtration, etc.), the vast majority of aquariums are struggling with the weak mineralization activity of bacteria. The plants then lack mainly the following nutrients: magnesium (Mg), potassium (K), and microelements mainly iron (Fe) and manganese (Mn).
  2. Algae always occur where there is poor activity of bacteria and where plants grow poorly. They arise from an excess of poorly decomposed organic substances that act toxic in the aquarium, and where plants have poor conditions (mainly CO2 deficiency).
  3. Excess of nitrates and phosphates, which may appear in well-filtered, inadequately planted and fish-overloaded tanks, are toxic to plants and may, under certain conditions, cause algal growth. However, I emphasize: in the analyzes, we found that algae often occur in aquariums where nitrate and phosphate levels are much lower than in aquariums where plants grew beautifully and algae did not occur. This means that there is no direct connection between nitrate levels and algae!
  4. Many aquarists claim that plants do not grow because they have too hard water (water with a high mineral content). But even this statement is not accurate. Plants, at least some species, do not grow in hard water not because it contains excess minerals, but because it has too high a pH [due to high levels of calcium (Ca) and carbonates]. This blocks the uptake of microelements and CO2. I recommend to the unbelievers to look for Bojnice [city], where [in carbonate thermal springs] not only grow, but thrive such plants as Cabomba or Rotala. The reason is simple. Thermal waters contain enough CO2 (mineral water) which lowers the pH so that it also suits these rather demanding plants.
  5. For basic measures to optimize plant nutrition, I consider quality biological filtration that prevents the accumulation of toxic organic waste and provide plants with nutrients.

Nobody likes to see algae in the aquarium. Their occurrence indicates that there is not everything in the tank as it should be. Why the algae suddenly appear in the aquarium is a question that trouble many aquarists.

The most frequently offered explanation is as follows. Algae appear in the aquarium due to excess nutrients, mainly nitrates. Nitrates are produced by the bacterial degradation of fish faeces and other organic residues. Let's just say, "I just have too many nutrients in the aquarium." But is it really so? The following observations do not suggest this:

In the experiment we described in detail above, we watched how the type of filter affects the amount of nutrients in the aquarium. To our surprise, we found that in most aquariums, nitrate concentrations did not increase, and yet algae were found in them. On the contrary, we measured intensive increase of organic substances in these tanks (measured as COD = chemical oxygen demand).

Organic substances seem to have a direct effect on algae:
At the beginningAfter 80 days
NO3 concentration45 ppm48 ppm
Amount of organics (COD)1.1 ppm4.8 ppm

Nitrates and phosphates do not have direct effect on algae:
Aquarium with algaeAquarium without algae
NO33 ppm3 ppm
PO40.08 ppm0.09 ppm

Based on the above experiments and observations, I would say that excess nitrates and other nutrients are not directly related to the occurrence of algae. On the contrary. If nutrients are added to the tank in a reasonable amount, the bacteria "burn" the organic residue in the tank well. These conditions are characterized by clear, slightly yellowish water, good plant growth and minimal algae presence.

If the activity of mineralizing bacteria is disturbed, there is an imperfect degradation of organic pollution, which begin to accumulate in the aquarium (the so-called COD increases as in our experiment). Organic residues act toxic to plants, which in addition lack nutrients, stop growth, turn yellow and rot. Water in the aquarium loses its clarity and algae begin to appear.

The imperfect activity of mineralizing bacteria and the consequent accumulation of toxic organic substances in the water
is therefore, in our opinion, the main reason for the appearance of algae in the aquarium!

So how to reduce the occurrence of algae in the aquarium? There are five aspects of aquarium operation:

  • Biological way of filtration and optimal fish load
  • Proper water change regime
  • Proper plant care
  • The use of certain fish and crustacean species (algae-eaters)
  • Chemical fight

"The proliferation of algae is often caused by the excessive amounts of organic matter in the water due to a poorly functioning biological filter. A good solution to reduce the load of a biological filter and remove organic substances that cause algae proliferation is to temporarily replace some of the filter media with activated carbon." (ADA)

Marcel Goliaš © 2019