Just fill up the syringe again and keep going til it changes colour... add the numbers from the chart together. This will give you a decent reading... could be that it's at 10000 ppm... 'over 1500' doesn't help a lot, only to tell it's not under 1500!Oh yeah idk about the mag. 1500 is as far as the salifert test reads. I empty the syringe and it still hasnt turned purple. Or blue.