Andy Hall wrote in message ...
Fernox DS-3 Limescale Remover is sulphamic acid and does a good
descaling job for taps, shower screens, bogs, kettles etc.......

Cost is about £8 for a 2kg tub.
The tub I bought a couple of years ago will probably last my grandchildren
into their old age.....
There was talk on here a while back that, although the crystals are
harmless, the solution is less so. I keep a tub of it handy to dunk the
shower head in overnight.