Anthea, I use a little less sugar (about 300g) and I don't make the tea so strong- 6 spoons of loose leaf green tea in a muslin bag, waved around lightly for 15 minutes in about 3 litres of boiled water, NEVER squeezed!. It no longer fizzes so much and is a lot more predictable and tasty. At the moment I've also got the fermenting jar sat on an upturned wicker basket, inside which is a heater pad that gives off a very low amount of heat. The whole lot is then insulated with towels. I'll try to remember to take a photo.
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Co-leader of the Kombucha Kurious & Fond of Fermenting Sparkteam. www.pauldale.info