All about TAC, TH and TDS

TAC, TH, TDS and pH are the 3 main factors that make up water balance. Understanding them better will allow you to keep your water clear all season long. To enlighten you and help you differentiate between them, find all the information you need to remember in this article. 


What is the difference between TAC, TDS and TH?

Here are some definitions to help understand these three related but often confused indicators:

  • TAC: alkalinity rate (concentration of carbonates and bicarbonates, hydroxide ions)
  • TH: hydrotimetric rate (water hardness, calcium and magnesium ion concentration)
  • TDS: Total Dissolved Solids, this is the most 'complete' of the three values as it includes all dissolved solids.

What is the TAC?

The TAC, or Total Alkalinity Content, determines the alkalinity of water by measuring the concentration of carbonate and bicarbonate ions.  This measurement indicates the ability of the water to absorb pH fluctuations and stabilise the pH.  The unit of measurement for the TAC level is ppm (parts per million) or French degrees (°F). By regulating the TAC level of your water (TAC+ or TAC-), you can do what is called "buffering your water". The pH value of the water will be stable.

All about TH

The TH or Hydrotimetric Title corresponds to the hardness of the water, which designates its concentration in limestone. It is measured in French degrees (°F) and is ideal between 10 and 20°F. The higher the TH, the harder the water, i.e. the more calcareous it is. On the contrary, the lower the TH, the softer the water.

What is TDS ?

ICO measures the TDS (Total Dissolved Solids) level every hour, which is the concentration of trace elements (iron, chlorine, bromine) and minerals (calcium, phosphates or carbonates). If the TDS is too high, it will be responsible for the appearance of limescale which will cloud the water and damage the equipment to the point of causing the appearance of algae. Conversely, if the TDS is too low, the water can irritate the skin and eyes. Watch the video below to learn more about TDS

vidéo youtube Ondilo vidéo chimie tout savoir sur le TDS, le TH et le TAC

Reminder on the pH of your pool/spa water

The pH is the acidity of the water and is measured on a scale of 0 to 14. The pH of drinking water is usually between 6.5 and 8.5. However, the pH of your pool should be between 7 and 7.4.

The pH is assessed on 3 levels:

  1. A pH below 6.5 means that your water is acidicacide
  2. A pH of 7 means your water is neutral
  3. A pH above 7.6 means your water is basic

To know all bout pH, read this article.