All about water hardness (TH)

The hardness of the water in your pool is measured with the TH. Water that is too hard, with an excess of limescale, is dangerous for pool and spa equipment. Conversely, water that is too soft leads to corrosion of metals and walls. Here's our advice on how to measure and treat your pool water effectively. Just like pH and TAC, TH must be monitored to maintain balanced water.

The hardness of water is measured with the TH, responsible for the water balance.

How is water hardness measured?

Water hardness is measured with TH ( Hydrotimetric Titer) which corresponds to the concentration of calcium and magnesium mineral salts. Hardness is expressed in ppm (or mg/L) or in French degrees must be between 10°f and 20°f (100 to 200 mg/l or ppm).

Below 10°f : the water is too soft, which can lead to problems with corrosion of metal parts and cements. To identify water that is too soft, do this simple test: take a sample of water from your pond and put it in a bowl. Try lathering it up with soap. The more foam, the softer the water and the less foam, the harder your water.

Above 20°f: the water is too hard. The water becomes cloudy and milky. Limescale quickly deposits on the liner at the water line and on the equipment (filtration, ladders, and pipes). This hard water is also irritating to the skin and eyes. Water hardness depends on the region you live in.

Water hardness in your area: how can you tell if your water is hard?

It's important to know the quality and hardness of the water in your area when monitoring your pool and spa water. Depending on this criterion, you'll need to adapt your treatments throughout the year.

To obtain the hardness index of the water in your community, you can:

  • Consult the official water quality data of your country
  • Go to the town hall, which should display this data.
  • Look at your water bill, the ARS of your region makes a synthesis of the water quality of your region annually and indicates it on this bill.

Which solutions to analyze the TH?

Before treating water with the right dosage, you need to analyze the three main factors responsible for water balance: pH, TAC and TH. To measure TH, suitable colorimetric strips are commercially available.

  • Certains appareils de dernières générations, comme ICO analyse le TDS (Total des Solides dissous), grâce à sa sonde de conductivité qui mesure l’ensemble des minéraux (calcium, bicarbonates) et des oligo-éléments (chlore, brome ….).
  • The TDS is between 250 and 2000 ppm for pools treated with chlorine or bromine, and between 3000 and 5000 for pools treated with salt.

How to reduce water hardness?

As mentioned in the previous paragraph, water is said to be too hard when the TH is above 20°f or (100 to 200 mg/l or ppm).

  • First, keep an eye on your pool's water temperature. To reduce it, increase filtration time and add shading above your pool if necessary. A high water temperature promotes the formation of limescale.
  • Secondly, regulate your pool's pH(between 7.2 and 7.4 for a chlorine-treated pool).
  • Finally, you can add a lime sequestering product to slow down the formation of lime.

How to increase water hardness?

Water is too soft when the TH is below 10°f. Here's how to increase it:

  • Start by balancing the pH of the water by adding ph+.
  • Once balanced, complete the treatment with calcium chloride (TH +) to raise the TH to 15°f.
  • If the TH measured is abnormally low,
    • If you have a swimming pool, you can also use calcium hypochlorite, which is the most powerful product for increasing TH.
    • If you have a spa, it may be a good idea to take advantage of the quarterly water change to renew the water and avoid using expensive chemical treatments. 

Treating water that's too soft or too hard isn't so difficult

To enjoy your pool or spa with peace of mind, you need to know the water hardness in your area so you can adapt your maintenance and chemical treatment routine throughout the year. TH is one of the values you should measure regularly to check water balance. This is particularly recommended if you find that you're having trouble maintaining a balanced pH, the cause of which may be water that's too hard or too soft.