Magnesium higher than salt mix

[jlado13]

I have a mixed reef Waterbox 15 nano, and am researching dosing for my growing SPS frags.  I will post a build thread in the near future.  Here’s my question...

 

Why/how would my actual tank’s magnesium readings be HIGHER than my freshly mixed batch of saltwater?  Freshly mixed = heated/mixed for several hours.  I use Instant Ocean Reef Crystals.

 

Advertised = 1440 magnesium.  

Freshly mixed batch after several hours of heating/mixing = 1260-1290 magnesium.

My tank = 1410 -1440 magnesium depending on when readings are taken throughout the week.

 

I use Salifert test kits and have tested over and over, reading instructions along each time and have duplicated the above results.  It seems the numbers are correct once mixed in with my tank, but what’s up with the low readings on the fresh batch?

 

Thanks,

Jordan

[seabass]

Reef Crystals isn't always consistent.  Some batches will be different from others.  You might also notice that levels aren't always consistent throughout the batch (often thought to be due to settling during shipping).  Inconsistency throughout the batch can sometimes be corrected by rolling the bucket on the floor, to help redistribute the contents.  This isn't just a RC thing (although it seems to be a relatively common complaint), other mixes can also experience these same issues.