Hiya, tried Barkeepers Friend while visiting sis in Canada and it's the only really effective thing I found to work on my toilet scale after trying the usual round of CLR, vinegar. In Canada it costs $3 so of course it's six times that here. Available at Plumbing World. I was using the pour on at her place, tried the powder at mine. Google says it has Feldspar* Oxalic Acid. Citric Acid. Polymeric Dispersant*
Also, CLR over there worked great on scale (took a ton off my sister's bathtub, tiles, faucets and toilets and got them as-new) but over here what should be the same product is a different colour and ineffective at least for me. I emailed the CLR people asking if it was different and got no response.