I have recently become a proud new owner of a 1500 litre hot tub and also a new member to the forum. I have been investigating the Dichlor/Bleach method and getting various chemicals ready for my 1 month water change that is recommended for a new tub. I believe I can source everything needed, except the hydrochloric acid seems to be sold in 36.2% strength in the UK instead of 31.45% that the pool calculator's calculations are based on. Do I simply adjust the ml recommended by the calculator by a factor of 15% since 36.2 is 15% more than 31.45? In other words if the pool calculator recommended 100ml of hydrochloric acid at 31.45% would this be the equivalent of 85ml in a 36.2% strength solution?