@Rasta Roy
I've had this discussion with many on the topic..All the 'purists' wont use agsil16h because of potassium carbonate.
Which is understandable, potassium carbonate has been stripped down and is indefinitely in its final salt form- as the hydro-heaven likes to call it- Potash!
A little info..
Potassium - 32%
Silica (SiO2) - 52.8%
0.7 grams in 1 gallon of water yields 49 ppm Potassium and 98 ppm SiO2 [or 46 ppm of Si]
To convert these amounts to percentage;
49 ~ 10,000 = 0.0049% Potassium
98 ~ 10,000 = 0.0098% Silicon
For Agsil 16 we can therefore state that;
0.7 grams in 1 gallon = 0.0049% K & 0.0098% SiO2
Given this percentage of potash, I've concluded that I'd definitely need to worry more about what's in my tap water, soft rock phosphate, or azomite..
Yoda, rice collects a great abundance of silica. Using the hulls in your mix will give you a good alternative as well.