Water Temperature & Chemistry

Most tropical brackish water fish will do at temperatures of 20 to 25° C (68 to 77° F). A few species appreciate slightly warmer conditions, for example archerfish and bumblebee gobies prefer the temperature to be not less than 25° C (77° F). When using an aquarium heater, ensure that you are using one that is safe in salt water -- some are not.

Fishes from the temperate zones will not do well at tropical temperatures for long. While many species will adapt to ambient room temperature provided the oxygenation of the water is adequate, other species may require a chiller, particularly in summer. Aim for a temperature of around 15° C (59° F) and certainly no higher than 18° C (65° F).

Fish from slightly brackish water (such as kribensis and spiny eels) are generally not picky about pH or hardness provided extremes are avoided. A slightly acidic to neutral pH with low to moderate hardness appears to suit these fish best. Species from the more marine end of the spectrum, such as monos and scats, need hard, alkaline water conditions. Sea salt contains minerals that should harden the water and make it more alkaline, but at low salinities sea salt alone may not be adequate. A good way to ensure a high pH and hardness is to use calcaereous media in the filter, such as coral sand or crushed coral.

Using these as a substrate for an undergravel filter does work, but over time bacteria and algae coat the grains reducing their effectiveness. It is more reliable to place the calcareous media in a canister filter where it can be more easily removed, cleaned, or replaced.

Sea shells will also help to buffer the water. Do not use snail shells from the garden, garden pond, or anywhere else that you cannot be sure the shells have not been exposed to poisons such as insecticides and herbicides. Shells from the fishmongers or grocery store (such as oysters, scallops, and clams) can be used but clean thoroughly beforehand. Small quantities of meat are often left in the shell even after the shellfish has been prepared for eating, and these will decay in the aquarium. Small fish such as gobies are especially fond of shells and will use them as resting places and spawning sites.

Do not use dead corals in brackish water aquaria. Besides not being a natural part of brackish water ecosystems, many corals are threatened by over-collecting (among other pressures) and there are perfectly adquate artifical alternatives.

Bogwood can be used in brackish water aquaria, but it does tend to acidify the water. In tanks containing hard water this effect will be minimal, but the tannins released by the wood will still tint the water yellow or brown. This is not intrinsically bad, and some fish, such as glassfish, look especially nice in slightly coloured water.