1.026 SG has about 8% more ions than saltwater mixed at 1.024, so figure aprox 370 ppm calcium if you mixed it at 1.026. That pretty much matches what is expected out of the older batches of Instant Ocean. The place you bought your salt still may be stocking the older stuff.
If you buy a 200g box, that is the new formula. I'm not sure how to tell the new from old on buckets or smaller bags.