How do I lower high alkalinity in my pool?

What total alkalinity does

Total alkalinity (TA) is a measure of the dissolved minerals that buffer your water against pH changes. Think of it as a shock absorber for pH. The ideal range is 80 to 120 ppm.

When TA is above 120 ppm the buffer is too strong. pH keeps drifting upwards and becomes very hard to bring down, and you may see cloudy water, scale on tiles and heaters, and chlorine that does not seem to work.

Common causes

• Hard, alkaline tap water - many areas of southern and eastern England have high alkalinity straight from the tap.
• Too much alkalinity increaser or pH increaser.
• Liquid chlorine or calcium hypochlorite, which add alkalinity over time.
• A newly rendered or plastered pool.

How to lower alkalinity, step by step

There is no product that lowers alkalinity without also lowering pH. The standard method is to use pH reducer to push both down, then raise the pH back up with air, which does not add alkalinity back. It takes patience - usually a few days.

• Run the pump and keep it running.
• Using the app's plan or the label, add pH reducer to bring pH down to about 7.0-7.2. Dissolve it in a bucket of pool water first (chemical to water, never water to chemical) and pour it in the deep end, in front of a return.
• Never add it at the same time as chlorine or any other chemical.
• Aerate the water: point return jets upwards to break the surface, run fountains or waterfalls, or run hot tub jets and blowers with the cover off.
• After 24 hours retest. pH will have risen with the aeration while TA stays lower.
• Repeat until TA is back under 120 ppm, then stop and let pH settle at 7.2-7.6.

Preventing it coming back

Add alkalinity increaser in small doses and retest before adding more. If your tap water is very alkaline, top up with smaller amounts more often, and test after every large top-up. In a hot tub, draining and refilling every three months or so resets the balance.

When to call a professional

If TA is above 200 ppm and repeated treatments barely move it, a partial drain and refill may be quicker. Ask a pool professional before draining a pool - some pools, particularly in-ground pools with a high water table, must not be emptied.

Frequently asked questions