The Brackish Aquarium
In order to run and maintain a brackishwater aquarium, a combination of freshwater and marine aquarium equipment is needed. However, for the most part, maintaining a brackish aquarium is much the same as maintaining a freshwater aquarium. The key difference is the necessity of marine salt and a hydrometer. While a refractometer can be used in stead of a hydrometer, salt levels in brackish aquaria do not need to be as exact as they would need to be in a reef aquarium. In fact, it is generally accepted that fluctuations in salinity levels actually benefit the health of aquarium fish.
The size of the aquarium needs to be large enough to comfortably deal with the bio-load of the livestock and the livestock themselves, keeping in mind requirements and temperaments of the fish or invertebrates. The most common brackish fish available are medium to large size fish that are fast swimmers with high waste outputs. Due to this aquariums with a larger surface area are recommended to allow for easier movement in the aquarium and dilution of waste. For a beginner aquarist, an aquarium with a minimum size of 40USg is advised.
Types of Aquaria
There are three basic types of brackishwater aquaria:
- Fish Only (FO)
- Half & Half (HH)[Paludarium]
Fish Only - Fish only aquariums are aquariums that only contain fish. These aquariums lack invertebrates and plants that would otherwise be found in the brackishwater biome. Often FO aquariums require minimal lighting compared to planted and HH aquariums. The main decor in these tanks are rocks. Often a couple of large granite rocks are incorporated with a few small river rocks in order to replicate a rocky shore or brackish river bed. Tufa rock is not advised as it quickly develops an unsightly brownish coloring.
Planted - Planted brackish aquariums are as their namesake, planted. Planted aquariums require a lower specific gravity (SG) of salt in order for plants to thrive. A SG of around 1.003 will suffice for this purpose, while plants native to brackish waters can generally be kept in a SG near 1.005. Keep in mind that brackishwater aquaria require "hard" alkaline water, so freshwater plants adapted to hard, alkaline water can often be easily acclimated to low end brackish water. It is recommended that a sand substrate is used for planted aquariums. Regular fertilization will be require in order for plants to thrive and it may be required to mix soil in with the lower reaches of the substrate. When the salinity is higher i.e. upper brackish, lower marine, macroalgae can be utilized in stead of true plants.
Half & Half - The HH aquarium is truly a brackish paludarium: half land and half water. HH aquaria are most commonly seen when mudskippers, four-eyed fish, crabs, and/or mangroves are being housed. The most popular themed HH aquarium is the mangrove biotope. Though their name implies exactly half water and land, the HH aquarium can either have more land then water or vice-versa. . HH aquariums often contain mangroves, rocks, wood (submerged and/or above water), and sand substrate. Sand is recommended when housing mudskippers due to the fact that rock and coarse substrate can be irritable for the fish.
Different species require different levels of pH, temperatures, and salinity. However in brackish aquatic systems, a general rule is to keep the water hard, alkaline and salty. The pH of the water should be no less then 7.5. Brackish fish available in the commercial trade are from the warm tropics of the earth and for this reason water temperature should be 75-80˚ Fahrenheit. Since the pH should be relatively high compared to freshwater aquaria and the water should be alkaline, a buffer of some sort as would be used in marine aquaria is advisable to help maintain this water quality.
Water in a brackish aquarium needs to be salty to a specific degree. Brackishwater fish do best in specific gravity between 1.005 to 1.015. Brackish water by definition covers a range of salinity levels that are between that of freshwater and marine and because of this "brackish" cannot be precisely defined, or rather there is not a specific SG that brackish is. Due to the wide range of salt content in the water brackish fish are best grouped into three relative categories: lower end brackish, true brackish (or just brackish) and upper end brackish.
The specific gravity of a true brackish aquarium is anywhere from 1.005-1.015 with a middling of around 1.010. True brackish is so called because it is home to "true" brackish fish i.e. figure eight puffers, knight gobies, archerfish, and monos. For this reason true brackish can also be called simply brackish. Lower end brackish aquaria tend to have freshwater fish that can tolerate low amounts of salt, while upper end brackish aquaria tend to have marine fish that tolerate a SG slightly lower then that of marine. While freshwater fish in low end brackish aquaria may look appealing, they are best left in freshwater. Likewise with marine fish in upper end brackish aquaria.
Equipment in brackish system combines that of freshwater and marine. Equipment needed to successfully maintain brackish aquaria are as follows: heater, hydrometer, marine salt, filter (mechanical and biological), substrate, light and some form of proper aeration. Optional are: sump, refugium and powerful lighting.
Filters & Filtration
Multiple sources of biological and mechanical filtration are recommended when running a brackish aquarium. The three main types of filtration in brackish aquaria are:
- Biological Filtration
- Mechanical Filtration
- Chemical Filtration
As in marine aquaria, refugium and sumps can be incorporated into the system to house live sand and rock. While some fish may benefit from fluctuating salt levels, biological bacteria may not and do not. For this reason changes in salt level should be minimal and it should be important to maintain stability in the aquarium. As for mechanical filtration, "hang on the back" filters often work well for brackishwater aquaria. In brackish aquariums, chemical filtration by use of carbon works well in removing dissolved elements in the water as well as the yellowish color that can develop in an aquarium over time.
Aeration & Circulation
Oxygen levels in aquaria are mainly affected by the surface area of the aquarium. Due to this tanks with a larger surface area are recommended. Aerators and powerheads are advised for increased surface disturbance and oxygenation of the water.
As with any aquatic system, for the most part good circulation is essential. For this, a power head or water pump will suffice. So called "dead spots" should not be allowed in the aquarium. Dead spots are where there is an area in the aquarium that lacks circulation and allows for the build up of detritus.
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