I used to have bb gobies and they slowly died over a 6 month period in a FW
tank. They are slow and are easily out-competed for food and they REALLY do need salt in their tank. I do not recommend adding marine salt to an established FW
tank. Bb gobies (and other BW fish) need the minerals found in marine salt, not regular aquarium salt. Some people will come on and say they have had "success" with keeping bb gobies in a FW
tank, but they are best to be kept in what they evolved to be in. Since bb gobies are sold usually as FW
, it is best to slowly acclimate them while they are in QT
. You can see pics of my established BW tank in my gallery. Many of my gobies have been with me for well over a year and they are active. A bb gobie that just sits at the bottom of the tank is not a healthy/"happy" bb gobie.