4) to dilute nitric acid produced by fish food and waste breaking down. The plants won't reduce nitric acid in water but by removing ammonia they will reduce the nitric acid build up so it won't happen as fast. Limestone and shells in the tank will help to neutralise the nitric acid.
Nitric acid in tanks is created by nitrate. Plants will use nitrate as will algae. If the nitrate is being used, nitric acid is not an issue. Similarly, nitrite will create nitrous acid in a tank. This is not real stable however, but it can cause issues. In a cycled tank, nitrous acid should not be a serious problem because nitrite does not accumulate. Also, when the plants and algae use ammonium, they do not create nitrate, the bacteria do this. So, the plants are using both ammonium and nitrate which means nitric acid is not normally an issue especiallyt tanks that get regular water changes. But I also know in tanks where I have mattenfilters that I have denirification hapening in the massive foam used for this kind of filter. No plants are in my tanks with Mattenfilters, but I do not have nitrate issues either. What I have inside the foam are facultative bacteria.
Basically, the cycle creates acid. Acid in water can cause the pH to drop. However, this is mitigated by the KH. In tanks most of KH comes from carbonates and bicarbonates. The nitrifying bacteria use these components as well as CO2 to provide the inorganic carbon they need. In addition, some plants can use the carbonates and bicarbonates as well as CO2. So without water changes these will become depleted sooner or later.
In the absence of water changes the buffering capacity will decline and the pH of the water will become increasingly more acidic. This is one of the most common problems in Old Tank Syndrome.
Water chemistry is complex. For example, plants use ammonium while the bacteria and Archaea use ammonia. When the plants use ammonium there is no nitrite or nitrate created. However, we do not want to be adding ammonium to our water to feed plants. And then there is the algae which also uses ammonium. And both plants and algae can use nitrate when ammonium is not present in enough amounts to satisfy their needs. In a cycled tank with plants and algae, nitrate is one of the primary sources of nitrogen for the plants and algae.
Also, if one has substrate of any depth, there is very little or no O below about an inch of depth. Most of the roots of substrate plants in our tanks are in anaerobic zones. But some plants in our tanks will actually transport oxygen down to their root where they release it in the anaerobic zone. The result is the presence of released O makes it possible for the nitrifying bacteria to function, which they do. And while they are using ammonia, they are also making nitrate. And then what happens is that zones above and below the roots develop denitrifying bacteria. There is as linking between the newly created aerobic areas and the new denitrifying areas.
Finally, the deeper one's substrate, the less circulation there will be with the depth. And there is plenty of research which discusses root feeding fromthe substrate and then fromt the water. The more food in the water the less that must be obtained from roots or vice versa.
All of the above is complicated by the fact that tap water parameters vary, plant needs and what they use varies and then water changes also effect the chemistry. My personal belief is that any give tank has its own unique chemistry. In some case we have tanks with pretty similar composition in terns of nutrients, minerals, trace elements etc. And then there are variables like stocking, feeding and maint. which also have an effect.
So the variables involved can vary greatly fromtank to tank. But the main protection put fish have against diseases etc. is their natural immunity. And this is not a universal. As long as the concentration of any pathogens are low, many fish can fight them off. But if the fish has it's immune system weakened by stress, poor nutrition etc., it can then succumb to what it would otherwise be able to fight off.
One good example is Ich. If a fish is attacked by this and manages to fight it off, with or without the aid of treatment, it tends to build an immunity against Ich. This is not a permanent state, but for some number of months it will be effective. This is why it is not uncommon when having an Ich outbreak in a tank, that some fish may not be infected while other fish are overwhelmed and some may actually die from this parasite.
Wang, Q., Yu, Y., Zhang, X. and Xu, Z., 2019. Immune responses of fish to Ichthyophthirius multifiliis (Ich): A model for understanding immunity against protozoan parasites.
Developmental & Comparative Immunology,
93, pp.93-102.
https://www.sciencedirect.com/science/article/abs/pii/S0145305X18304944
Abstract
The parasitic
ciliate Ichthyophthirius multifiliis (Ich), which infects almost all
freshwater fish species, provides an optimal model for the study of immunity against extracellular
protozoa. Ich invades the epithelia of
mucosal tissues, forms white spots covering the whole body, and induces high mortality, while survivor fish develop both innate and
adaptive immunity against Ich attack in systemic and
mucosal tissues. Besides the protective roles of the Toll-like receptor (TLR)-mediated innate immune response, the critical immune functions of novel IgT in the skin, gut, gill, and olfactory organ of teleosts have been demonstrated in recent years, and all this information contributes to the
ontogeny of the
mucosal immune response in vertebrates. Especially in
rainbow trout, Ich-infected fish exhibited higher IgT concentrations and titers in the
mucosa and increased IgT+ B-lymphocyte proliferation in mucosal tissues. IgM mainly functions in the adaptive immune response in the systemic tissues of
rainbow trout, accompanied with increased IgM+ B-lymphocyte proliferation in the
head kidney of Ich-infected trout. However, little is known about the interaction between these mucosal tissues and systemic immune organs and the interaction between the inductive immune organs and functional immune organs. Immobilization antigens (Iags), located on the parasite cell and ciliary membranes, have been characterized to be targeted by specific antibodies produced in the host. The crosslinking of antigens mediated by antibodies triggers either an escape response or the immobilization of Ich. With more knowledge about the Iags of Ich and the immunity of teleosts, a more targeted vaccine, even a
DNA vaccine, can be developed for the immune control strategy of Ich. Due to the high frequency of clinical fish ichthyophthiriasis, the study of fish immune responses to Ich provides an optimal experimental model for understanding immunity against extracellular
protozoa.
My point here is that it is difficult to make blanket assumptions about a lot of what goes on in our tanks that we cannot see nor measure. So it is important to understand how and why things work in natural water bodies but may not work in quite the same way in a tank. One is a natural environment v.s. an artificial one.
Nature works to deal with a lot of things which also occur in tanks. But there is not nature in a tank to fix imbalances. That must be done by us. What we can see is how our fish and inverts etc. are faring. If they are healthy, if they grow and reproduce as expected and if they live as long, or more often longer, than they do in nature, we are doing things right. If our fish are not healthy, if we are consntatly battling imbalances and/or diseases etc. it is because we are failing and not because of how nature works.
The best we can do is to understand the processes and the chemistry and biology involved and then try to use that knowledge help us to make our tanks healthy for the inhabitants. But every tank is unuique in its chemistry, stocking, tap water parameters and then how we care for the tank. While nature tends to be self sustaining, this is not how things work in our tanks. In them we are "nature: to a great exetent.
To be effective we need some level of knowledge about the science involved. And then we do water changes in FW tanks. We repelenish what us used up and we remove what potentially harmful things are building up. The one thing I do know here is that my fish do not die because thw water is too clean (not pure but free or mostly free from harmful things). As long as the water contains what is needed and does not contain harnful things at levels that natter, out tanks should be funxtioning decently for the inhabitants to thrive.
I never understand why hobbyists are intrigued with the idea of not having to do water changes as often and/or of great enough volume to achieve the desired goals. After all, we are not keeping tanks like in a public aquarium or in aquaculture ponds where the volume of water is so massive that water changes are not a realistic otpion.
One last observation re plants and the removal of contaminents from water. I would suggest one visit Google Scholar and the ask it about: "heavy metal uptake potential aquatic plants" here is the sort of thing you will discover. Plants can clear a lof of nasty sruff from water that many would not have expected.
Rezania, S., Taib, S.M., Din, M.F.M., Dahalan, F.A. and Kamyab, H., 2016. Comprehensive review on phytotechnology: heavy metals removal by diverse aquatic plants species from wastewater.
Journal of hazardous materials,
318, pp.587-599
https://www.sciencedirect.com/science/article/abs/pii/S0304389416306860
Abstract
Environmental pollution specifically water pollution is alarming both in the developed and developing countries. Heavy metal contamination of water resources is a critical issue which adversely affects humans, plants and animals.
Phytoremediation is a cost-effective remediation technology which able to treat heavy metal polluted sites. This environmental friendly method has been successfully implemented in constructed wetland (CWs) which is able to restore the aquatic biosystem naturally. Nowadays, many aquatic plant species are being investigated to determine their potential and effectiveness for phytoremediation application, especially high growth rate plants i.e. macrophytes. Based on the findings, phytofiltration (rhizofiltration) is the sole method which defined as heavy metals removal from water by aquatic plants. Due to specific morphology and higher growth rate, free-floating plants were more efficient to uptake heavy metals in comparison with submerged and emergent plants. In this review, the potential of wide range of aquatic plant species with main focus on four well known species (hyper-accumulators):
Pistia stratiotes, Eicchornia spp.
, Lemna spp. and
Salvinia spp. was investigated. Moreover, we discussed about the history, methods and future prospects in phytoremediation of heavy metals by aquatic plants comprehensively.
Plants etc. can even deal with radfioactiveity in water.
Vanhoudt, N., Vandenhove, H., Leys, N. and Janssen, P., 2018. Potential of higher plants, algae, and cyanobacteria for remediation of radioactively contaminated waters.
Chemosphere,
207, pp.239-254.
https://www.sciencedirect.com/science/article/abs/pii/S0045653518308762
Abstract
The potential of photosynthetic organisms to remediate radioactively
contaminated water was evaluated for scenarios related to nuclear installations and included the following
radionuclides............... An extensive literature review was undertaken leading to the creation of a database including more than 20,000 entries from over 100 references in which terrestrial and aquatic plants, macro- and microalgae, cyanobacteria and biosorbents derived from these organisms were used to clean water from these specific
radionuclides or their stable isotopes.....................Finally, the most promising organisms and biosorbents were identified using a specifically developed selection procedure taking into account their performance and robustness. Ranking was done based on clear criteria with a distinct weight and scoring scheme. As such, 20 organisms/biosorbents were identified that showed high potential to clean waters contaminated with (mixtures of) radionuclides related to nuclear installations and which can be used for further experimental investigations.
