Potassium chloride (kcl)

[asylumdown]

I'm holding a bottle of lab grade KCl in front of me that I just used to do a series of nitrate and ammonium extractions on a batch of soil samples for my masters. Since it's lab grade, it also lists it's impurities:

Iodide: 0.002%
Bromide: 0.01%
Chlorate and Nitrate (as NO3): 0.003%
Other Nitrogen compounds: 0.001%
Phosphate: 5ppm
Sulphate: 0.001%
Barium: 0.001%
Calcium, Magnesium and R2O3 precipitate: 0.005%
Heavy metals (as Pb): 5ppm
Iron: 3ppm
Sodium: 0.005%

I'm sure there are more pure forms of KCl available for higher level analytical chemistry, but that's what the University of Calgary considers to be 'Lab Grade'. I imagine the list of impurities for KCl that you can buy in the store or in bulk would either look similar, or be slightly to much worse. The chances that your'e going to get a KCl additive (or any kind of additive for that matter) that only adds KCl are pretty much zero. Not sure if any of those listed parameters would be enough to cause problems in a tank though, or which contaminants are likely to increase in concentration when you go with a lower grade salt.