Total Alkalinity (TA)

TA test kit

-   AKA 'TA' - is a measure of the total alkaline substances found in the pool water

  • Basically, it’s a measure of the dissolved bicarbonates
  • It’s in the same area as pH, but is distinct from it
  • In swimming pool water, we measure bicarbonate alkalinity, which should be between 80 - 120ppm
  • When TA is within this range, it prevents rapid pH changes and "stabilizes" the pH level
  • If the TA is too low, the grout between the tiles, or the top surface of the pool plaster will be gradually eaten away, metals will corrode, the pool's walls and floor can stain, the water can turn green, eyes will burn and we can have pH bounce (pH rapidly going up and down, seemingly at random)
  •  If the TA is too high, the pH is difficult to adjust, the water becomes cloudy, the Chlorine loses its effectiveness as a sanitizer and (according to your test kit) the pool constantly needs acid or pH-minus powder
  • eroded grout due to low TAIt is recommended that you test the TA monthly, but in practice it changes very little in a well-maintained pool
  • Most Reagent Test-kits do not measure for TA, but if you take a plastic bottle of water from your pool into a pool-shop or pharmacy they will be able to test TA for you
  • To raise the level of TA, use Sodium Bicarbonate; it is the only chemical which will do this without increasing the pH unduly
  • To raise the TA of your pool by 10 ppm use 700g of Sodium Bicarbonate for every 50m³ of water
  • Or 20oz of Sodium Bicarbonate for every 10.000 US Gals of water
  • Note: - you should add Sodium Bicarbonate at this rate every 4 days until the level is correct
  • Raising the TA can therefore be quite a time-consuming, slow process
  • If you just want to raise the TA,  pH-plus should not be used as it will affect pH also

Lowering the TA is also a slow process

Acid, either liquid or dry, is added to the deepest part of the pool with the pump and filter off

Add acid a little at a time, diluting or dissolving it before pouring it into the pool

Wait 3 days between applications. It could take weeks or even to reduce the TA if it is very high

To lower the TA of a 50 m³ pool by 10 ppm use 800ml of liquid Hydrochloric Acid at 30% concentration

Total Alkalinity remains too low

  • Likely cause - Bicarbonates in the pool are diluted by low-bicarbonate mains water when you top the pool up
  • This is common in soft water areas
  • Cure: - Add Sodium Bicarbonate to raise the total alkalinity to around 100ppm
  • A dose rate of 1.5kg per 50 m³/ 13.000 US Gals of pool water will raise the alkalinity level by 20ppm
  • Pre-dissolve the Sodium Bicarbonate and add to the pool via the skimmer with the pump on
  • Sodium Bicarbonate is the only chemical that can adjust Alkalinity upwards without affecting pH
  • Sodium Bicarbonate is generally cheaper at catering supply outlets than it is at a pool-shop

TA and Pool-covers

As outlined above, TA is a measure the total alkaline substances dissolved in the water, basically a measure of the dissolved solids (TDS) in the water

A pool-cover will greatly reduce evaporation, so your TA will take longer to rise and you won't need to fill the pool so often

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