good man. they will look so much better in brackish. and generally be better for it. not sure on the dats though, it depends on what species you have. google says "if you want to keep datnoids in brackish you would need to get D polota or D campbelli". but doesnt say anything about keeping them in full marine. i know the columbian shark cats will need high end brackish/full marine as adults though.
for brackish fish i'd say try BAS ut its a bit far from you. they generally have a healthy stock of brackish animals. they had barramundi last time i was there. cheap too.
any pics of your fish. this thread is useless witout pics