Very confused on params/test kits?

No, IO is 1350 @ 1.026. This is independently verified. However, test kits are not accurate, mg test kits only seem to be accurate to about 100ppm or so IME, some maybe more. So, this alone could almost explain it. Also, even with calibration fluid you could still be off by a little bit and salt isn't always perfectly consistent. So, really, I'm not sure it is that far out of range. You may want to try a different mg test kit. If the salt was off by 50ppm, your test kit off by 100ppm and your s.g. 1.027, you could get a reading of 1550 with IO. That is really not all that unlikely IMHO. I would still check with another mg test though if you are concerned.

 

Well, Red Sea Coral Pro Salt arrived in the mail yesterday, so I mixed up a batch and tested the mag... came out to 1400 @ 35ppt. Used the same method for calibrating the refracto (35ppt cal fluid) and same mixing procedures.

I guess the IO batch I had really was wacky.