After much rinsing I have done some tests. There is a bag of sand 17cmx18cm in about 10L of water and so far it's 4ppm KH and the Ph is the same as my test sample from the cory tank. The cory tank water has 6ppm KH. The sand behaves like silica sand, it stays flat and smooth. You can see grains of black, gold and dark brown. I am going to taste it and see if I can detect any salt.
Am going to leave it to sit overnight and retest it, then mix some with silica and/or EC sand to see if I can make the perfect colour. A bag of this stuff at Central landscaping is $6.10 and it's the same size bag as the river pebbles. I may have enough in my sample to darken up mine without needing to buy more too heehee
Oh and I meant to say they also have big river pebbles, a few as big as my head, many fist sized and larger. I think you can also buy by the bag full or I'm sure they will let you buy only as many as you need. They do offer samples of everything too.
EDIT - water in bucket doesn't taste at all of salt 8)