The calcium level in tap water from the Edwards Aquifer is around 175 ppm.
That's something that I haven't mentioned in all the recent "my calcium is to high" posts we have seen recently. If you are getting about 525 ppm from Oceanic salt and you are using tap water that would give you a total of about 700 ppm of calcium. If you are using that water to do water changes that doesn't have a very high calcium demand it would be easy to see some of the 600+ ppm calcium test results that have been reported. That would also apply, to a lesser degree with water coming from an RO unit with exhausted cartridges or a membrane that is overdue for replacement.
Gary
125 SPS, 75 gal. LPS/softie reef, 9 gal. Nano