Cu – Copper in aquarium water.
One of the most toxic heavy metals, yet it is included in many medications for aquarium fish. Metallic copper is moderately toxic to fish, while its soluble salts (chlorides, nitrates) are toxic already at a concentration of 0.01-0.02 mg/l. The toxic effect of copper salts is more pronounced in soft water, because in hard water part of the copper binds as carbonates. It is extremely toxic and poorly removed from plants and the aquarium. Even in small concentrations, copper is able to kill aquarium bacteria and invertebrates as it damages respiratory systems.
Copper will kill crabs, crayfish, shrimp, snails, and significantly damage the bacterial colony formed in the substrate, requiring time for its recovery. The biological balance will be severely disrupted, which can lead to algae outbreaks. Excess copper causes chlorosis in plants. Copper accumulates in the leaves and stems of plants, and they will slowly turn black and die. Fish tolerate higher concentrations of copper, but in soft water, the risk of toxicosis increases. Later, copper forms compounds and deposits as a thick white coating on aquarium equipment, suction cups, heaters, hoses, and in the filter.
Ideally, copper should not be detectable by tests in aquarium water. Unfortunately, sometimes this metal is present in tap water. Aquarium decorations and substrate can also release copper. Also, try not to use copper wire to secure plants and equipment in the aquarium. Let copper remain only in fish medications used when necessary and in a separate quarantine tank, under test control. It can only be used in a separate container. It is absolutely necessary to always measure the pH level before adding medications to the aquarium. The effectiveness of copper decreases with an increase in pH and organic matter in the aquarium.
Before using the product, remove invertebrates from the aquarium. It is recommended to transfer fish to a separate container during treatment and subject them to treatment with this remedy there. Precise dosage must be used. Upon completion of treatment, a partial water change should be carried out. Plants can be treated before planting in the aquarium by keeping them in a vessel with 0.2 mg/l copper sulfate. After treatment, free copper must be removed by a partial water change. After that, filtration through activated carbon is necessary.
Fe – Iron in aquarium water.
In houses with old water pipes, water is “enriched” with rust, which does not add health to fish and plants. The admixture of iron makes itself known by a rusty taste and characteristic traces on the surfaces of toilets, bathtubs, and sinks. Along with chlorine and ammonia, tap water may contain nitrates as well as excess iron. The toxicity of iron compounds depends on pH. In alkaline water, toxicity to fish increases sharply because iron hydroxides are formed, which settle on the gills, clogging and corroding them. In addition, Fe(II) easily turns into Fe(III), which binds the oxygen dissolved in the water, leading to mass mortality of fish.
Excess iron is harmful because it can lead to the appearance of algae, especially hair algae. High concentrations of iron are also harmful to fish. When there is too much iron in the water, its compounds can settle on the fish’s gills as a brown coating, interfering with their breathing. Water containing iron is unsuitable for incubating fish eggs because its hydroxide settles on them and the fry’s gills, causing their death. Mollusks are very sensitive to iron. To remove excess iron, you need to dissolve a little manganese in the water. With powerful aeration, the content of iron and manganese in the water decreases noticeably.
Carbon and iron play the main role in plant nutrition. An exceptionally high level of various trace elements, such as iron, magnesium, and manganese, stimulates the formation of chlorophyll, which makes the leaves of aquarium plants bright green. But sometimes unfavorable or unsatisfactory conditions for plant growth are created in the aquarium. With a lack of iron, plants suffer from chlorosis. Plants starve and often slowly die. The reason for these phenomena is the incomplete assimilation of carbon and iron salts by plants. This happens when soluble iron salts turn into an insoluble state right inside plant cells. Iron is best consumed by plants in the form of chelate and gluconate.
Ensuring normal iron nutrition is one of the most important tasks in the cultivation of aquatic plants. The characteristic signs of this “iron chlorosis” disease are that the plant lags in growth, wrinkled leaves turn yellow, become glassy, and die. These signs are most noticeable on young leaves and fast-growing plants. Chlorophyll is formed in leaves in the light, which plays the role of an energy carrier in this case, and in the presence of soluble iron salts in the cells as a catalyst. Various complex fertilizers containing iron are commercially available. They supply aquarium plants with ferrous nutritional iron, providing their leaves with fresh lush greenery. Symptoms of deficiency disease, such as yellow pale leaves, immediately disappear; young leaves appearing on the plants are colored with a rich green color again. It is important not to exceed the dose recommended by the manufacturer, otherwise you risk destroying the aquarium. At pH above 8, iron turns into insoluble hydroxides.
PO4 – Phosphates in aquarium water.
Phosphates are compounds of phosphorus (salts of phosphoric acids). Phosphates are organic and inorganic. They are present in various amounts in any aquarium. Sources of phosphates in the aquarium: • excessive feeding with flake foods; accumulated fish waste not consumed by plants and not removed by regular substrate vacuuming; • dead fish not removed from the aquarium; • decaying plant leaves; • expired carbon filter media; • lowering pH using phosphoric acid; • sometimes tap water contains a lot of phosphates.
Phosphates, even in large quantities, are not toxic to fish. But they can lead to rapid algae growth, which sooner or later negatively affects higher plants and fish. In aquariums with many actively growing higher plants, the problem of phosphate accumulation usually does not arise – plants readily consume phosphates. Usually – because plants assimilate organic phosphates only after their mineralization. Therefore, it is advisable to test water for phosphate content even in aquariums with live plants. There should be no zero nitrate level in the aquarium. Usually, at a zero nitrate level, the phosphate level in the water begins to rise after a few days. When nitrates are added, it drops to zero again. Carbon does not remove nitrates and phosphates, which are one of the main problems of algae appearance in the aquarium. Water changes are one of the main ways to combat algae (reducing phosphate concentration).
Try to avoid using carbon from drinking water filters. Carbon used for drinking water filters is rinsed in phosphate-containing acids. It has a low pH value, so it will “acidify” the water and release phosphates that promote algae growth. Be careful when using brand-name pH-minus preparations, as the latter are made on the basis of phosphoric acid. Unfortunately, the use of phosphoric acid has a side effect – an increase in phosphate levels in the aquarium. And as we know from practice, phosphates in water stimulate the growth of simple algae.
Water color in the aquarium. Why does the water turn green and “bloom” in the aquarium?
Cl – Chlorine in aquarium water. 
