I should have mentioned it's labeled play sand & no there is no mention of mineral content. Peter said in his book to use play sand. We have free sand available right out of the pits, I grabbed a couple handfuls Friday night. I did a little test with my TDS meter, the pit sand was 117, the play sand had a reading of 87. Later (after I dumped it) I thought I should see when adding the peat what that might do, so took a handful of each (play sand/peat) and the reading dropped to 47. That should be be OK, my husband also suggested, although it would be a bit inconvenient, to wash the play sand .... here goes another experiment!