that people use supplements that are made by manufacturers with a history of quality. Many use a GMP seal, (meaning good manufacturing processes).
There is a website that evaluates supplements and it is
called Consumerlab.com
they will share for free some info, but you have to join and pay a small yearly fee for details, of their tests.
http://www.consumerlab.com/
Many people can obtain what they need thru food, and I always suggest foods as sources of nutrients.
For example... 3 oz of unsalted almonds have about 270mg of magnesium in them.
This website offers excellent information about food choices...
http://www.nutritiondata.com/
If you check websites of the various vitamin/mineral makers, you can find ones that do very careful quality control.
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All truths are easy to understand once they are discovered; the point is to discover them.-- Galileo Galilei
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Weezie looking at petunias 8.25.2017
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