Hello,
Brackish aquaria are not difficult to run. The only extra things you'll need are salt and a hydrometer. It is important to decide on the specific gravity (SG, the "saltiness") that you are aiming for. Freshwater has an SG of 1 and seawater has an SG of about 1.020. Brackish water is somewhere in between, typically 1.005 to 1.010. Some fish prefer a low SG, for example orange chromides and archerfish, while others need a high SG, such as scats and monos. Freshwater soles are almost always brackish water soles -- there are some true freshwater species, but they are rarely sold in Europe and almost never sold in the US. If you're in the US, then almost certainly the soles you are being offered as
Trinectes maculatus or
Achirus lineatus.
As a general rule, brackish water fish are hardy but more sensitive to low oxygen concentrations, so be careful not to overcrowd them. You need to maintain a high pH, so minimise or avoid using things that acidify water, such as peat.
Freshwater soles ("flounders") are difficult fish for beginners. They need a sandy substrate (silica sand or river sand) and
not gravel. This is because they are diggers; fish that dig into gravel damage themselves and the wounds get infected by bacteria. Sandy substrates cannot be used with undergravel filters. An external canister filter is probably ideal. Don't put anything sharp in the tank, like coral or rough stones, because the soles can scratch themselves on them. Smooth stones like cobbles are best.
Next thing to worry about is food. They are nocturnal predators, and top begin with you need to give them
live foods such as tubifex and bloodworms
at night. If you don't do this, it will starve and then die. After a few weeks they will take frozen bloodworms and even catfish pellets, but again, these need to be given at night.
Use a normal temperature (around 24 C).
Plants are problematical with brackish water because only a small selection work well, and even then, only at an SG of 1.005 or less. Plants are difficult to grow unless you have strong lighting and a good substrate; read up on how to look after plants first. If in doubt, leave them out. Although soles dig, they don't damage plants. It's important to make sure there are lots of open spaces for them though.
Read the posts on this site about soles to learn more. Also visit the Brackish FAQ (see the link below) for more on the basics of brackish and some tips on identifying which species you have.
Cheers,
Neale
Brackish FAQ, freshwater soles section
Brackish FAQ, start
