Home Aquarium Fish Tank with different type of fish, like Molly, Angel, Barb, etc.....
The cycle refers to the conversion of toxic ammonia to nitrite and finally nitrate. While fish waste (urine and feces) and decaying matter release ammonia, the majority of ammonia released (approximately 60%) in both marine and freshwater aquariums is excreted directly into the water from the fishes' gills. Biological (bacterial) nitrification converts the ammonia into nitrite ions, NO2-, and then to nitrate ions, NO3-. Nitrate is readily taken up and assimilated by algae and hermatypic corals. Some nitrate is converted via an anaerobic bacterial process to free nitrogen, but this process is very difficult to maintain. In the recent past, most nitrate, which is less toxic to fishes and most invertebrates than nitrites, accumulated in the water until it was physically removed by a water change. However, many marine aquarists are now employing the use of a special section of the tank or separate tank altogether, called a "refugium." A refugium is, as its name suggests, a sheltered area that shares water with the primary, or display, tank. Refugiums usually contain a deep sand bed to allow anoxic zones to develop within them where anaerobic bacteria can convert nitrate into nitrogen gas, a useful means of nitrate removal. Various types of macroalgae can be grown and harvested from the refugium as another means of nitrate export. As refugiums become more common in marine aquaria, nitrate levels are easily manageable for even the novice hobbyist. Ammonia and nitrite should be tested regularly; any detectable levels (i.e., over 0 ppm) can be indicative of a problem. Nitrates should not exceed 2 ppm in reef tanks, or 20 ppm in fish-only tanks. It is sometimes acceptable to have a small amount of nitrate buildup, as some livestock, especially fish, are fairly tolerant of nitrate. Most corals, while able to assimilate nitrate, cannot be expected to survive, much less thrive, with high nitrate concentrations.
When considering lighting for an aquarium, there are generally two factors to consider: wattage and color temperature. Depending on the type of lighting (i.e. fluorescents, metal halide, etc.) the wattage of light emitted may vary considerably, from tens of watts to several hundred watts in a lighting system. Wattage, while not indicative of color, is equivalent to power and essentially determines how brightly the light will shine. Due to the scattering of light in water, the deeper one's tank is, the more powerful the lighting required. Color temperature, measured in (albeit slightly unrepresentively) refers to the color of light being emitted by the lamp and is based on the concept of radiation. Light from the sun has a color temperature of approximately 5900 K and lighting systems with color temperatures >5000 K tend to be best for growing plants in both the marine and freshwater setting. 10,000 K light appears bluish-white and emphasizes coloration in fishes and corals. Higher up on the spectrum there are 14,000 K and 20,000 K bulbs that produce a deep blue tint which mimic the lighting conditions underseas, creating an optimal ambience for invertebrates and livestock present.
Aquarium fish - a look at the popular types of fish tank additions
Common Types of Freshwater Aquarium Fish - YouTube