Low Total Alkalinity (also known as TAC) can make it difficult to maintain the pH of your hot tub water between 7.2 and 7.6.  Use HTH pH stabiliser to increase the total alkalinity of your spa water and (surprise!) to stabilise its pH. If you have soft tap water, we recommend that you add 100-200g of HTH pH stabiliser each time you refill your spa.

HTH pH stabiliser contains sodium bicarbonate, which also makes the spa water feel softer on your skin.