Again, I agree with sweet tang.
I would empty it all out, and wash it out with tap water, and let it dry completely before filling again. Specially if you have used any copper based treatments when it was FW (whitespot treatment, for example).
Then, fill with RO and salt, and warm it up. You might as well use RO, specially for the first set up, to make sure there is as little nutrients entering the water as possible (phosphate, nitrate etc).