Water Chemistry

Info provided by Latham Pools

Fiberglass Pools Use & Care Manual

There are two primary systems involved in maintaining water purity: the water chemistry system and the filtration system. Both of these systems must perform properly; one cannot be substituted for the other.

When you fill your pool for the first time, the water may appear cloudy or turbid. Don’t be alarmed. Since your pool is filled with drinking water, the same water you use in your home, you assume it is sparkling clear. Appearances can deceive. In small amounts, such as a glassful, most tap water will indeed appear clear. In much larger amounts, such as a full pool, that clarity often disappears.

Water which is perfectly acceptable for household use may be totally unacceptable for your pool. This is the reason your pool water must be professionally tested and balanced every six to eight weeks.

There are five basic steps of water chemistry to be performed at home. They are as follows:

Step 1: pH Control

pH, which is the measure of acidity or alkalinity of the water, is determined by your test kit. Proper pH maintenance is extremely important as it is responsible for the correct bacterial action of the chlorine, swimmer comfort and prevents deterioration of the equipment and the pool itself. A proper pH reading is 7.4 to 7.6. Ideally, your pool should be maintained at the higher level of 7.6.

After testing the water, if the pH is too high (above 7.76), chlorine efficiency is reduced, scaling of the surfaces and equipment may occur, water may become cloudy, and shorter filter runs may occur. To correct this condition, a pH decreaser is added directly to the water. There are two common forms of pH decreaser: liquid muriatic acid and granular sodium bisulfate (Lo N Slo, pH Down, pH Minus). The granular form is the one recommended for your pool. Never add more than one pound of sodium bisulfate or one pint of muriatic acid per 10,000 gallons of pool water without professional guidance.

If the pH is too low (below 7.4), chlorine dissipates more rapidly, water may be irritating to swimmers, and corrosion of equipment and surfaces may occur. To correct this situation pH increaser is added directly to the water. pH increaser (BalancePak 200, pH Plus, pH Up) is commonly called soda ash. Never add more than one pound of pH increaser per 10,000 gallons of pool water without professional guidance.

Step 2: Continuous Disinfection

Chlorine treatment is to maintain water purity. A good average chlorine residual is 1.0 ppm. The pool may be carried as low as 0.6 ppm or as high as 2.0 ppm. The lower level would be more subject to system failure and the higher level would increase operational costs. Therefore, the recommendation of a 1.0 ppm operating level is a good compromise that will assure water purity and low operating costs.

The use of compressed tri-chloro-s-trazine-trione, (Bio Guard Stingy Sticks, TabGard Tablets, Sun Sticks, Sun Tablets, etc.) insures even levels of continuous chlorination. Usage rates will be approximately one half to one pound of chlorine per 10,000 gallons of pool water per week. As with any pool chemical, follow the use directions on the container. Never mix different types of chlorine.

Step 3: Super Chlorination

Super chlorinating or shock the pool is a chemical treatment to eliminate non filterable wastes from the pool water. A granular chlorine product such as calcium hypochlorite (Burn Out 65, Shock Out), lithium hypochlorite (Burn Out 35, litho-Shock), or sodium-dichlor-s-trazine-trione-dihydrates (Sun Booster) is used to obtain a chlorine reading of 8.0 to 10.0 ppm. Super chlorinating chemicals are available in convenient one pound packages or in bulk packages of 25 to 75 pounds.

Calcium hypochlorite should always be pre-dissolved before adding it to a fiberglass pool to prevent bleaching or staining of the surfaces. Calcium hypochlorite is used at a rate of one pound per 10,000 gallons of pool water.

Lithium hypochlrite is a quicker dissolving chemical which may be added directly to a fiberglass pool. It is used at a rate of one pound per 6,000 gallons of pool water. 

Sodium di-chloro, like lithium hypochlorite, may be added directly to the pool. It is used at a rate of one pound per 10,000 gallons of pool water.

Step 4: Prevention of Algae

Contaminants in the rain and wind can quickly deplete the chlorine supplies in the pool. A high quality algaecide (Algae Inhibitor, Algaecide Concentrate) acts as a chemical back up system in the event the chlorine becomes exhausted from the pool.

Following a one time initial treatment (normally one quart per 25,000 gallons of pool water) add a maintenance treatment (normally two ounces per 5,000 gallons of pool water) directly to the pool every other week or every week.

Step 5: Prevention of Staining

In order to prevent staining of the interior pool walls, a metal chelation product (Pool Magnet, Metal Hold, Metal Magnet) is used. This product aids in the removal of metals introduced to the pool by fill waters, rain, and corrosion of metal equipment.

Following an initial treatment (normally one quart per 10,000 gallons of pool water) metal chelation products are added on an every other week basis (normally two ounces per 5,000 gallons of pool water). Never add this product with a shock treatment.