We tend to use Elsil in the Aquaroll to keep the water and pipework sweet.
I have found that it can be quite difficult to obtain from dealers and there wasn't even any at the Manchester Caravan Show.
Managed to locate some from Boroughbridge Marina via Amazon at a very reasonable price.
Elsil via Amazon
They charge £5 plus 18p delivery when other sources,including E-Bay are charging £7,£8 £9 and even £10 plus postage in some cases.
So if you want some then that is the place to go.
I have no association with Boroughbridge Marina.