I keep mine fresh as well
they grow and spawn at a regular date, but the eggs get eaten by other fish.
IF you want to keep them brackish -wich is perfectly possible- use seasalt, the kind for marine tanks.
and don't overdo it; it's a brackish, but not a marine fish.
salt with extra added iodine isn't good for fish. it's harmless to use in saltbath cures for ich and the like, but for permanent use, best use the stuff the reefkeepers use.
a brackish tank with grandidieri might be very nice to look at; you could combine it with Etroplus suratensis, Scats and Hexanematichthys seemanni ("Arius jordani", Silver Shark catfish).
"And he piled upon the whale's white hump the sum of all the rage and hate felt by his whole race. If his chest had been a cannon, he would have shot his heart upon it"