Fish, Fish and More Fish on Lombard and Divisadero sells both RO/DI and fresh sea water. They highly recommend the seawater. I use my own unit though. It saves plenty of money over time.
One question for you TDS users:
I used to read about 96 to 100 PPM at the tap, 10 to 12 after RO and 0 after DI.
My meter now reads about 56 to 60 at tap, 3 to 5 after RO and 0 after DI.
Now do you think my meter is off or has San Francisco improved the quality of their water?