On 16 Feb, 17:29, Stuart Noble wrote:

Citric acid was 69p for 150 gms last time I looked. A tablespoon should
be plenty

So long as you use it in time. Citric acid won't shift really thick
scale once it's built up - then you're back to the sulphamic and the
formic.

Personally I didn't mind thick scale so much, as it stayed where it
was and I could descale it from time to time. The stuff that really
annoyed was thin scale that was brittle enough to flake off the
element end up in my tea.