Thanks for all your feedback. It sounds like i've got a barrel full of weed killer. The recipe I started with (courtesy of an ABC website) said add two camden tablets per 5 litres of juice and leave for 12 hours before adding yeast.
I googled camden tablets and found a conversion rate to SO2...
So I built a hand press and pressed my own apples. Got 18 litres of juice to which i added 2 tablespoons of SO2 sterilising powder to kill wild yeasts.
I topped up my brewing vessel with 6 litres of purchased natural juice. Then added a sachet of Wyeast Cider Yeast.
Left the lid off for 12...