Minerals and trace elements necessary for fish.
Minerals are absolutely essential for skeletal development (calcium and phosphorus) and healthy fish growth. A fundamental difference between aquarium fish and invertebrates compared to land animals is that mineral substances and vitamins can enter their bodies not only through food or drinking, but also directly from the surrounding water — through the gills and body surfaces. Fish living in hard water can extract calcium from the water, but fish living in soft water require more calcium in their diet. Such a condition can lead to stunted growth and health issues in fish.
Minerals are necessary for the formation of body tissues, especially bones and cartilage. The most important ones, such as sodium, potassium, calcium, and magnesium, are absorbed directly from the water, while certain trace elements like iron, copper, zinc, manganese, and cobalt are integrated in sufficient quantities from a diverse diet. Calcium and phosphorus are often lacking in soft water. However, the action of calcium is only expressed in the presence of vitamin D. Calcium, potassium, and other minerals render oxalic acid ineffective. Since green vegetables sometimes contain a high concentration of this acid, a diet too rich in vegetables can lead to calcium deficiency in fish.
Fish and plants select necessary trace elements from the water, which leads to their systematic depletion in aquarium water. Among other important elements, manganese, iron, zinc, etc., can be noted. They are needed in very small quantities. Usually, herbivorous fish obtain these minerals along with plants and algae.
Trace elements play various roles in the body. They affect growth, reproduction, hematopoiesis, etc. The body’s demand for trace elements, as their name implies, is very low, but the organism cannot exist without them. There are over 30 trace elements — metals and non-metals. A deficiency of trace elements, particularly iron, leads to anemia, lordosis, scoliosis, skull deformations, and convulsions.
Taking advantage of this, aquarists often solve the problem of providing their pets with these substances by adding them not only to foods, but also directly to the aquarium water. A deficiency of trace elements, particularly iron, leads to anemia, lordosis, scoliosis, skull deformations, and convulsions.
Water changes are a way to add trace elements to a planted aquarium if you are not fertilizing them. It is better to change water more frequently (e.g., once a week) but in smaller portions (10-20% of the aquarium volume) than rarely and in large amounts. This prevents drastic water parameter changes that can cause stress in fish. Proper aquatic plant cultivation also requires the daily addition of trace elements and, especially, iron-containing fertilizers. Among the methods for purifying water from chlorine, boiling or heating to 80-90°C is also mentioned. Boiling makes water “dead” in terms of useful trace element content and drastically reduces carbonate hardness.
Trace elements in the substrate. The only way to deliver trace elements to plants is to prevent their oxidation and precipitation. Plants receive trace elements in two 
ways — through the water and the root system. In both plant nutrient sources, trace elements must be in a bound state. In water, trace elements must be dissolved, meaning they must have a specific ionic state [X2+] to be utilized by plants. Otherwise, they oxidize very rapidly into [X3+] and can no longer be used by plants for nutrition, as they will be removed from the solution, i.e., precipitated.
For example, ferrous iron [Fe2+] is extremely reactive, and in oxygen-rich substrate forms iron oxide and hydroxide (trivalent Fe3+) and precipitates as rust without ever being utilized by plants. Trace elements that behave similarly are iron [Fe2+], calcium [Ca2+], magnesium [Mg2+], sodium [Na+], potassium [K2+], manganese [Mn2+], zinc [Zn2+], copper [Cu2+], and even ammonium [NH4+].
To be available for plant nutrition through water, the listed trace elements must be chemically bound by chelators to remain in a dissolved state, i.e., having the appropriate ionic divalent state [X2+]. For chelating trace elements in liquid fertilizers, chelators like HEDTA and DTPA are used, which bind, for example, iron as Fe3+, or gluconate, which binds iron in the form of Fe2+.
The availability of iron [Fe] and other macro- and microelements for plant nutrition depends on the amount of oxygen in the substrate. Too much oxygen will quickly oxidize trace element chelates, and they will precipitate without ever being used by plants. Almost all oxygen in the substrate must be consumed by aerobic bacteria living in the substrate. They will consume all oxygen only if they are present in sufficient quantities.
For the bacterial colony to work at its maximum capacity, conditions must be such that the surface area of the substrate for bacterial colonization and oxygen are in abundance, while nutrients from organic decomposition products are always lacking — the colony must be starving.
A large population of bacteria can develop only in a coarse, porous substrate with a very large surface area, such as lava rock, gravelite, etc. Due to a grain size of 8-12 mm, there is always a slight water movement between the lava particles, delivering oxygen for bacterial activity and nutrients for plants.
Depending on the plants’ nutrient requirements, loam and clay can be added to the sand (without mixing), as well as laterite soil sold in pet stores (which usually already contains added trace elements) to increase the nutrient reserves for plants. A reserve of nutrients and trace elements (for a period of 1-3 years) right in the substrate makes it possible in the first month or two to completely abandon liquid fertilizers except for potassium, which during this period can only promote algae growth.
Cavernous sandstone is very rich in trace elements such as iron, aluminum, barium, cobalt, chromium, copper, nickel, vanadium, manganese, zinc, etc. Such a rich composition benefits both plants and aquarium inhabitants. It has been observed that in an aquarium set up with sandstone, plants grew magnificently without additional fertilizer supplements!
Source of trace elements — add JBL Florapol, which provides a supply of iron and all trace elements for three years. Alternatively, use hard balls like JBL The 7 Balls or The 7+13 Balls. You can also apply pastes such as Aqua Medic ferropur (Fe+Mg), ferreal+spureal (Fe+all micros), and floreal+iod (fluoride+Fe+K+Mg+organics, added in addition to ferreal). Frits (FTE) can also be applied, for example Carl Pool’s Hibiscus Food — 2 teaspoons per 40×40 cm of bottom area, or Micronized iron (contains only iron) — a dose of 1/8 tsp per 40×40 cm. The best source of phosphates for the substrate is water-insoluble rock phosphate.
An aquarium is a closed space, and improper application of fertilizers or trace elements can quickly drive the concentration of any element beyond the limits useful to plants: the additive will become dangerous for aquarium inhabitants and even for the plants themselves. An excess of macroelements can lead to rampant algae growth and deterioration of the aquarium’s biochemical regime.
Vitamins, Minerals, and Trace Elements in Fish Foods.
Vitamin Supplements for Fish. Water-soluble and Fat-soluble Vitamins. 
