Common Causes of Pool Chemistry Problems

While the recommended ranges for these chemicals are essentially the same for every pool, the work that goes into maintaining them can vary significantly from pool to pool. Developing an understanding of what makes your pool different from another takes time and effort. Below is a list of common factors that vary between pools, and some of the possible effects of these variances. It is not an exhaustive list – it is only meant to serve as a starting point for understanding what makes your pool unique.

Pool Volume:

Having an estimate of a pool’s volume allows one to calculate how much of a chemical must be added to reach the desired concentration. It would also allow calculation of how much water needs to be replaced if sanitizer, hardness, or TDS need to be reduced. A key understanding is that contaminants from bathers or other sources will be more concentrated in smaller pools, meaning that adjustments need to be made more regularly.

Source (Fill) Water:

Depending on where source water comes from (e.g. city water, a well, a lake), differences in the characteristics like calcium hardness (or other mineral content), total dissolved solids (TDS), and even organic load will be seen from pool to pool. Having source water high in the mentioned characteristics will change how dilution influences your water chemistry, and other steps / products may be required. It is a great idea to know the quirks of the fill water.

Bather Load:

The number of people using a pool and how often it is used is called bather load. A higher bather load will require more frequent maintenance of water chemistry. Contaminants from bathers’ natural skin oils, and suntan / skincare products affect the pH and chlorine residual in a pool. In addition, when pool water leaves the pool (from splashing, cannonballs, etc.) and is replaced with fill water, it is likely the concentrations of calcium and stabilizer will be affected. It is good practice to increase the frequency of chemical checks when your pool’s bather load periodically increases (e.g. during a heatwave, having parties or houseguests, a new fitness routine).

Sun Exposure:

Ultraviolet (UV) light is the number one factor that decreases the chlorine concentration in a pool – especially if not stabilized. A pool in full sun will need to replenish chlorine more frequently than a pool that is shaded. Higher sun exposure also increases evaporation of pool water, meaning water will need to be replaced more often. Evaporation followed by refilling will cause changes in chemicals’ concentrations.

Water Temperature:

Water temperature in a heated pool is largely a matter of personal preference, and in an unheated pool is related to the ambient temperature and sun exposure of the pool. It is recommended to maintain a water temperature between 26 and 28 °C (78 to 82 F). A higher water temperature is associated with more rapid changes in water chemistry, especially pH. CO2 is constantly off-gassing from a pool, which gradually raises pH over time. This happens more rapidly at higher temperatures. pH will need adjustment more often during hot weather, and alkalinity should be checked more often.

The Pool Cover:

There are a handful of different pool cover types, ranging from low-tech solar pool covers, to anchored safety covers, to higher tech automatic pool covers. Covering a pool affects three main things: evaporation of pool water, off-gassing of chlorine and CO2, and water temperature. For specifics on how a pool cover can affect a pool, see the section “Covering and Closing Your Pool.”

Surrounding Environment:

Your pool does not exist in a vacuum! Environmental factors ranging from trees and grass around the pool to nearby farms may affect the pool water. Organic matter – living things like grass, leaves, or bugs – entering the pool by any means will increase the organic load of the water. What is more, organics may deposit stains on the liner if not cleaned out quickly. Chemicals used in your yard, or on a neighbor’s yard/farm may also get into the pool water. Fertilizers may be organic (like manure) or inorganic in nature (nitrates, phosphates) and can influence organic load or scaling of the pool, respectively.