Uhh! You have just answered your own question!! Read the Calgon box and all shall be revealed. On a tangent note: unless your water is near soft I do not, in my expeience, think Calgon makes much difference. I have been to houses over 36 years in the trade and people tell me they use this stuff religiously but still have limescale issues. The way of preventing lime build-up, given the modern washing machine water levels are pathetically too low, is to descale using 1 box of `Aqua Softna` crystals every 6 weeks in hard water areas such as my neck of the woods – Caversham. My machine is 18 years old owned by me for 16 years and is 90{e5d1b7155a01ef1f3b9c9968eaba33524ee81600d00d4be2b4d93ac2e58cec2d} spotless.