i think no salt if more better for the fish. if the freshwater salinity have, the fish disease is more harder to cure. what mean by freshwater fish ? = is no taste and no higher or lower ph. actually, salt is not compulsory for freshwater. the compulsory thing is the anti clorin medicine. high clorin will kill fish. if you get what do the guppy needs, it is very very easy to keep like ikan longkang. hehehe!! i keep before but the next day already died cause eating by my Ikan Kap. hahahaha!!!! to buy guppy, buy guppy where it come from thailand. very beautiful than local. but seldom to see lar.