Diatomeae, Bacillariophyta (Phaeophyta), Brown and Quartz Algae.
(Diatoms, Brown Diatom Algae).
Description. Diatoms (from Greek diatomos – cut in half). Diatoms are microscopic (0.75-1500 µm), unicellular, or colonial forms. Among the latter, there are species living in mucous tubes, forming brown bushes up to 20 cm high. Their cells have a hard siliceous frustule, they contain yellow-brown photosynthetic pigments due to their ability to accumulate a significant amount of silicon oxide in their organism, which gives the algae a brown hue.
They consist of two halves – the lower (hypotheca) and the upper (epitheca). Their outer shell is very hard and resembles a shell. The walls of the shell have pores through which metabolism with the external environment is carried out. Diatoms reproduce by division. Each daughter cell receives half of the parent shell, and the other grows anew, with the old half overlapping the new one with its edges.
Due to this method of division and the fact that the silica-impregnated hard shells have little or no ability to grow further, diatoms gradually become smaller as they 
reproduce. The latter form unattractive-looking brown coatings in shaded areas of the aquarium. Many diatoms, which have a slit-like opening (the so-called raphe) along each half of the shell, are able to move along the substrate, apparently due to mucus secretion. Algae that settle in aquariums generally have a rounded shape and are very dense to the touch. There are also green algae here – these are green patches against the general brown background.
Brown algae appear in the early stages of aquarium development. In aquariums, we mostly see diatoms on surfaces such as aquarium glass, rocks, ceramics, plastic, substrate, and they cover the leaves of plants. Brown algae spread in the form of dense flat formations. They form a dense dark brown or brown coating, tightly connected to the base, covering the substrate (most often), aquarium walls, and plant leaves. They spoil the appearance of the aquarium, giving it a dirty look, shade the leaves of higher plants, and disrupt their nutrition. They usually appear in partial shade. It creates the impression that sand is scattered over the glass and plant leaves.
Diatoms are lovers of diffused lighting. They are the first to settle in aquariums in insufficiently lit places. Once in suitable conditions, they can cause a lot of grief to the aquarist. If you do not fight diatoms, they will rapidly cover everything in the aquarium with a brown-brown mucous mass. The algae attach very tightly to the surface, and it is not difficult to remove them with a scraper or sponge at an early stage, but it is practically impossible from plants, and fish eat them poorly. But then red and green algae grow on this coating, and the situation becomes complicated. In such aquariums, plants also fall ill. Their leaves and stems turn pale, yellow, become thin, flabby, and begin to rot.
It is quite possible that you will notice a thin brown layer on the glass, rocks, substrate, leaves, thermometer, and other places a couple of days after filling a new aquarium under weak lighting. They quickly cover all surfaces of leaves, driftwood, and glass. In most cases, these are quartz algae. Over time, they will disappear completely. These “brown algae” are easily removed from the glass with a scraper or foam sponge. They appear in limited quantities and automatically disappear as soon as plants begin to properly root and optimal oxygen concentrations are established in the aquarium.
Causes. When green algae are replaced by brown algae on glass, equipment, and plants, it indicates that the aquarium is poorly lit. The appearance of brown algae in the aquarium is a sign of insufficient lighting and high silicate release from the new substrate. Their presence indicates a high level of silicates in the aquarium, as their cells contain a lot of silicon. Brown algae appear in the aquarium at high pH values (above 7.5).
They usually appear in a young aquarium during the first month. Thus, diatoms are the first to settle in aquariums in insufficiently lit places. Brown algae often appear in winter in aquariums devoid of artificial lighting. It has been noted that diatoms grow intensively in neglected aquariums with weak and short lighting. They die when lighting is increased.
Brown algae appear in the early stages of aquarium development; this is a brown fouling that covers everything from walls and driftwood to plant leaves with a thin film, disrupting their nutrition. If this is the only reason for the appearance of these algae, they will disappear on their own after some time.
Their appearance in a recently launched aquarium is considered normal. Excess nutrients and organics, the water may have a high content of organic carbon and NO2, and at the same time a low level of NO3 and PO4. In such conditions, brown diatoms feel just fine. Algae blooms also frequently occur in water with too high iodine levels. Therefore, we advise checking the chemical composition of any aquarium supplements you use – many of them contain a significant amount of iodine. In an older aquarium, the appearance of diatoms indicates either a severe lack of light or a very high level of silicates in the water.
Brown diatoms cause silicate levels to rise. Silicates may be present in your tap water and can cause a number of problems. Many aquarists believe that sand or other silicon-containing substrates can cause brown diatom blooms. To avoid this problem, first of all, we advise purchasing special water tests and testing your tap water to prevent problems in the future. If the dissolved silicate level in your water is at a medium level (3-4 ppm), you may see brown algae appearing in the lower, poorly lit part of the aquarium. Replacing regular tap water with water purified using a reverse osmosis system will help solve this problem. There is also another option to clean water from silicates – using phosphate-removing substances (they also remove silicates).
Their appearance is especially promoted by a too short period of low-intensity aquarium lighting of 6-8 hours a day. If you supply CO2, you need more light. If the light is normal, the reason is only an excess of silicates in the water. They need to be removed by water changes or special absorbent pads in the filter. In cases where such a coating appears constantly, it will be necessary to use a filter capable of absorbing silicic acid salts – silicates.
Control methods. The only way to prevent the appearance of these lower aquatic organisms and their reproduction in the aquarium is to maintain the correct regime in it. First of all, lighting must be sufficient, increasing lighting intensity (by adding lamps with the correct spectrum), and water temperature should not be lower than 24-25°C. Correctly selected lighting power and sufficient daylight hours will not only get rid of brown algae, but also prevent their appearance in the future. It is imperative to maintain cleanliness and regularly change water. Under such a regime, diatoms get many stronger competitors that suppress their growth. Conventional cleaning methods are ineffective.
You should fight these algae as follows: clean aquarium glass and equipment from them with a scraper, gently remove the film from plant leaves with your fingers, and use a hose to remove dirt accumulated during cleaning from the bottom of the aquarium. If this does not help, the next step may be to use a silicate-absorbing filter. In the food chain of diatoms, in addition to phosphates, nitrates NO3 can also participate. If you reduce the concentration of phosphates / nitrates and silicates in the water by frequent water changes, lower the pH by supplying CO2, these algae will quickly leave.
Biological control is quite effective. Various species of fish can also be assistants in the fight against brown algae. Fish and mollusks can only partially damage these foulings. You can simply get rid of them using natural enemies of these algae, the best of which is Otocinclus affinis. Plecos (Ancistrus) also eat diatoms well, but can damage delicate leaves. Gyrinocheilidae and Siamese algae eaters (SAE) also eat brown algae, but grow too large for a small aquarium and can ruin the composition. Most mollusks cope well with these algae. Horned nerite snails and olive nerite snails do a good job with this, as they also actively eat diatoms.
The use of any chemicals and antibiotics to combat brown algae is impractical. To prevent and provide long-term prevention of algae, it is recommended to use Algetten – these are slow-dissolving water tablets. To combat diatoms, some experts recommend antibiotics (bicillin-5, penicillin). Copper and zinc also destroy brown algae.
Red Algae, Black Beard Algae, Black Brush Algae, Red Brush Algae.
Methods of control against blue-green algae. 
