How Much Ppm Gives 1 Gram Of Amonium Nitrate In One Liter Of Water?

So I have amonium nitrate and added one gram to one liter of water and the PPM meter showed 1.5 ES and 750 PPM. My water is 50 PPM so the reading should have been 50 + 350 PPMs. From where the hell come the other 350 PPM?

This is the same with almost all chemicals I tested. Pottasium hydroxide gave me like 1800 PPM which I think is impossible one gram to contain more thant 1000 PPM. Oddly enough pottasium chloride gave me the right reading - around 900 PPM.
 
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