The factors that contribute to water balance are free chlorine, pH, total alkalinity, cyanuric acid, total dissolved solids and calcium hardness. Understanding what is considered the “preferred ranges” and how the chemicals behave will make the enjoyment of your spa that much easier.
First let’s start with the “preferred ranges”. They are as follows:
Free chlorine 2 -4 ppm
pH 7.2 – 7.6
Total Alkalinity 80 – 120 ppm
Cyanuric Acid 60 – 80 ppm
Total Dissolved Solids 0 - 1500 ppm
Calcium Hardness 150 - 250 ppm
First let me explain the types of chlorine, free chlorine, combined chlorine and total chlorine.
Free chlorine (FC) is chlorine that is available to combine with contaminates in the water to disinfect and sanitize the water. Free chlorine may also be referred to as residual chlorine.
Combined chlorine (CC) is after it has bonded with contaminants. In this state, it is no longer able to continue its sanitizing effect. It has done its job and must wait for additional chlorine to come in to continue to disinfect the water. The unpleasant smells and side effects often associated with chlorine are actually caused by combined chlorine.
Total chlorine (TC) is the total amount of chlorine in the spa, that is, the sum of both the free chlorine and the combined chlorine that holds the dirt, oil, and other compounds that make the water dirty.
pH has the most impact on properly balanced water and user comfort. The recommended pH of spa water is slightly alkaline (7.2-7.4). The ideal range to assist in user comfort is 7.4 to 7.6. Many things can have an effect on the pH of a spa, including: user waste; disinfectants; source water; air-borne debris; water balance chemicals; aeration; evaporation.
pH Related Spa Problems
Low pH High pH
Corrosive Water Scaling Water
Etching of spa surface Clogged filters
Corrosion of metals Clogged heater elements
Staining of surface walls Reduced circulation
Chlorine loss Cloudy water
Eye/skin irritation Chlorine inefficiency
To lower pH you can use muriatic acid or dry acid. To raise the pH you would use soda ash. Control of the pH is important for the comfort of the bather and the efficiency of the chlorine, as well as the protection of the system components. The method used to control pH is to maintain proper levels of the Total alkalinity (TA).
Total alkalinity (TA) is a measure of the water’s ability to resist changes in the pH. TA is like an anchor for keeping the pH where it should be. Without proper buffering of the TA, the pH can have dramatic swings from High to Low – these are known as “pH bounce”. At higher levels of TA the pH is usually higher than ideal and may become difficult to adjust – this may be referred to as “pH lock”.
Low TA High TA
Chlorine inefficiency Cloudy water
Corrosion Clogged filters
Staining Clogged heater elements
Eye/skin irritation Reduced circulation
To increase the TA level you can use baking soda. TA is lowered by using muriatic acid. Knowing that the adjustments of TA can have an effect on the pH levels it is always best to make large adjustments in a couple of steps, testing the water after each adjustment.
Cyanuric acid (CYA) is often referred to as stabilizer or conditioner. It acts as a sunscreen to protect the FC from sunlight. In doing this, it decreases the effectiveness of the chlorine in the spa. You need a higher level of chlorine in the spa to compensate for the CYA and maintain the same level of sanitation.
CYA comes from 3 sources: tri-chlor (chlorine tabs or pucks), di-chlor (granulated chlorine, also sold as shock) or directly from CYA. Over time the CYA levels can build as CYA remains even after the chlorine from the tri-chlor or di-chlor has dissipated. CYA is in essences a dissolved solid so once it is added it will remain. The only way to remove/reduce the CYA is to dilute your spa water by draining and adding fresh water.
Total Dissolved Solids (TDS) is as the name implies a measure of the total amount of dissolved material in the water. Testing for TDS is done by assessing the electrical conductivity of the water with an electronic meter.
TDS comes from many of the chemicals we use to keep our spas in balance. Every time you adjust the pH, add conditioner, algaecides, or chlorines, the TDS elevate. As the TDS levels climb above the recommended 1500 ppm your water may become cloudy and your chemicals become less effective.
The higher water temperatures and aeration in spas result in water evaporating at a faster rate than pools. This however does not remove the minerals or TDS in the water. As the TDS levels increase, chlorine may become less effective. This usually results cloudy water. The heater elements are more easily attacked by the spa water chemistry and unsightly staining may occur.
To reduce the TDS level the most practical solution is to drain some water and replace it with fresh water.