The Perma-Guard website has this to say about it:
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"Diatomaceous Earth used in pool (any water) filtration contains Diatomaceous Earth that has been chemically treated and heated making the silica crystalline which is a dangerous respiratory hazard and lethal if ingested. The fresh water naturally occurring Diatomaceous Earth deposits that are designated "Food Grade" by the FDA have less than 1% crystalline silica and all other sediment that are considered unsafe are also below harmful limits. These deposits are primarily Amorphous Silica which is harmless when ingested and is commonly used in feed and food industries."
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The difference is that Food Grade D.E. is fresh water diatoms that resemble little perforated cylinders under the microscope and most pool grade D.E. is processed salt water diatoms that resemble pieces of microscopic glass snowflakes crushed to the required size fragments. Pool Grade D.E. will interlock to form a very good filter bed.
Food grade D.E. does not interlock like pool grade and will not form a filter bed. It is finer and rounder than a sand filter will stop so it slides on through and clouds up the pool.
If you have both types of D.E., be sure to keep them separate and well labeled, and above all DON'T BREATH THE DUST and dispose of it properly.
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"Diatomaceous Earth used in pool (any water) filtration contains Diatomaceous Earth that has been chemically treated and heated making the silica crystalline which is a dangerous respiratory hazard and lethal if ingested. The fresh water naturally occurring Diatomaceous Earth deposits that are designated "Food Grade" by the FDA have less than 1% crystalline silica and all other sediment that are considered unsafe are also below harmful limits. These deposits are primarily Amorphous Silica which is harmless when ingested and is commonly used in feed and food industries."
______________________________________________________________________________________________________________________________________________________
The difference is that Food Grade D.E. is fresh water diatoms that resemble little perforated cylinders under the microscope and most pool grade D.E. is processed salt water diatoms that resemble pieces of microscopic glass snowflakes crushed to the required size fragments. Pool Grade D.E. will interlock to form a very good filter bed.
Food grade D.E. does not interlock like pool grade and will not form a filter bed. It is finer and rounder than a sand filter will stop so it slides on through and clouds up the pool.
If you have both types of D.E., be sure to keep them separate and well labeled, and above all DON'T BREATH THE DUST and dispose of it properly.