What pH should a hot tub be?

7.2-7.6 for hot tubs using chlorine or bromine. Stay below 7.8 to keep sanitiser effective.

Does pH minus also lower alkalinity?

Yes. Sodium bisulphate lowers both pH and total alkalinity at roughly the same rate.

How long until I can bathe after dosing?

Wait 60 minutes with the pump running, then retest. If pH is in band you can bathe.

Why dry acid instead of liquid muriatic acid?

Granules are safer to store and transport, do not give off fumes, and are easier to dose precisely in domestic settings.

How much will 5 kg cover?

Roughly 80-100 typical doses for a 1500 L hot tub or 12 months of monthly maintenance for a 30 m3 pool.

Can it be used in salt-water pools?

Yes. Salt chlorinators run pH high, so you will use pH minus more often than with a tablet system.

Why does chlorine work better at lower pH?

Chlorine exists as hypochlorous acid (HOCl) below pH 7.5 and as hypochlorite ion (OCl-) above. HOCl is roughly 80 times more effective at killing bacteria.

Does sodium bisulphate raise sulphates?

Yes, each 100 g per 1000 L adds about 80 ppm sulphate. Refresh part of the water if sulphates exceed 300 ppm.

Why should I dose half then retest?

Heated water reacts faster than expected. Half-dosing prevents pH crashing below 7.0 and avoids etching.

Add an equal weight of pH plus (sodium carbonate) to neutralise; retest after 60 minutes.

Why does my pH keep climbing back?

Either total alkalinity is above 150 ppm or carbonates are dosed in via tap water. Lower TA first to fix the drift.

Why is foam appearing after I lowered pH?

Acidified water can release dissolved organics into foam. Add Foam Away at 25 ml per 1000 L and clean the filter.

pH minus (sodium bisulphate) lowers pH and TA. pH plus (sodium carbonate) raises pH with little TA effect.

pH minus vs muriatic acid?

Same chemistry, different form. Muriatic acid is faster but more hazardous to handle. Sodium bisulphate is the domestic-safe equivalent.

pH & Alkalinity Reducer - Sodium Bisulphate

Name: pH & Alkalinity Reducer - Sodium Bisulphate
Brand: ClearSpa
SKU: wb-2
Availability: InStock
Rating: 5.0 (7 reviews)

Lower hot tub or pool pH safely with sodium bisulphate (dry acid). Brings high pH down into the 7.2-7.6 sanitiser-effective band without the fumes of liquid acid.

Reduces pH by approximately 0.2 units per 16 g per 1000 L.
Lowers total alkalinity at the same time, so dose carefully.
Restores chlorine and bromine sanitising power, which collapses above pH 8.
Prevents calcium scale forming on heaters, jets and waterline tiles.
Eliminates skin and eye irritation caused by alkaline water.