(first of all : sorry for follwing mistakes, english isn't my mothertounge, I'm from Germany)
Okay, on topic- to get excellent, crispy, chewable white ice, which I also like best, try this:
I always freeze sparkling(!) springwater in a metal cooking pot, the freezer has to be very cold.
I usually take 1 to 1,5 litres of sparklingwater for one cookingpot and it takes ca. 5 hours to become excellent, easy- chewable ice (of course you have to make little icepieces out of the big iceblock before you can enjoy..mmmhh) .