Silica Question

Are these the same? Can the second be used? Its a lot cheaper

Silicon Dioxide and Potassium Dioxide - http://www.kelp4less.com/shop/silica/#.UP-3BSfBd_B

Silica, Quartz, Crystalline Silica, Si02 "read MSDS"- http://www.axner.com/silica-200mesh.aspx

Another option... hope I don't confuse you

http://www.kelp4less.com/shop/diatomaceous-earth/#.UP_BCCdEGSp

That's cheaper than the first silica. It is also "food grade". I don't know about the pottery stuff. I use a little DE mixed into my substrate - I don't add an silica in my nutrients and water.