I have used it without problems in the past - in fact when I set up my 90 gallon almost all the water I used for the first fill was from the Gulf, half of the initial fill for my 180 was also from the Gulf. On both of those tanks I would say I did a Gulf water change with them about 1x/month for the first few months - other 2-3 were artificial salt water. I never did anything to the water except keep it circulating and heated it if needed. That said, however, the water was collected well offshore in blue water and used within 24 hours. The only reason I don't use it more often now is that it is considerably more work to get it since we don't live on the Gulf, just have a cottage there ..... so collecting it on the boat, transferring it to containers in the truck to take home ...... just simpler to mix the salt next to the tank!:ohwell:
I still have the 90 and a 300 gallon now and still do use the Gulf water once in awhile. I'm sure there are risks to it but personally I'm willing to take them - I figure it is just as good as our man-made water for the tank and I think it adds something beneficial to the enclosed system - everything has always responded positively to it. If it was easier I would use it all the time.