When to Change Pool Water: Water Saving Tips

Every chemical you add to the pool, minerals coming with the filling water and content condensing with evaporation increases the TDS value. This value can be thought of as a fatigue indicator that shows how 'filled' the water is.

TDS does not cause problems up to a certain level. However, when it gets too high, the effectiveness of the chemicals decreases, the water becomes dull, a salty feeling may occur and it becomes difficult to keep the balance. As a general practice, a significant increase in TDS compared to the filling water (e.g. several thousand ppm) indicates that some of the water needs to be replenished. Since salt is also included in TDS in pools using salt chlorine generators, TDS is naturally higher in these pools and the evaluation should be made accordingly. The correct reference is always the difference between the TDS of the filling water used and the TDS of the pool water.

However, in most cases, complete replacement is unnecessary and a serious waste of water. Partial water change, that is, removing some of the water and replacing it with fresh water (dilution), is a much more economical and effective way to reduce accumulated TDS and calcium. The proportion of fresh water is calculated based on the difference between the current TDS and the target.

A full water change is only required in certain circumstances: if TDS and calcium have become too high to reasonably be reduced by partial dilution, if there is serious and persistent water degradation, permanent stain or uncontrollable fouling, or if a technical intervention such as surface repair requires draining the pond. Apart from this, small partial changes at regular intervals save both water and heated water energy compared to a large one-time drain.

The main trigger is the significant increase in TDS relative to the filling water and, accordingly, the chemicals no longer easily maintain the expected balance. The second trigger is when the calcium hardness becomes too high to be reduced except by partial dilution. Third, stabilizers such as cyanuric acid accumulate excessively and begin to suppress chlorine effectiveness.

The practical approach is to keep water in balance 'before it goes bad, not when it goes bad'. Monitoring TDS and calcium trends with regular water tests allows you to foresee when partial replacement is required. The beginning and end of the season are natural checkpoints. In busy months, intermediate measurements are valuable. Water exchange is integral to good water chemistry management. In a pool that keeps the daily pH and chlorine balance correct, water tires much more slowly and the need for changes becomes less frequent.

Using a pool cover (tarpaulin) significantly reduces evaporation, especially in hot and windy climates. This saves both water, heated water and chemicals. The second step is not to unnecessarily increase the frequency of backwashing. Washing the filter only when the pressure gauge requires it reduces the amount of water expelled with each wash. Filter media that consume less water, such as glass or zeolite, also provide an advantage at this point.

The third step is to opt for partial dilution rather than complete decantation. Small calculated changes use much less water than large one-time drains. The fourth step is to proactively manage water chemistry. Getting the balance right from the start reduces the need for excessive chemical additions and the resulting premature water replenishment. Leak control is also important. An unnoticed leak silently leads to massive water loss. These cost-saving practices are a natural part of regular pool maintenance and provide both environmental and economic benefits in the long term.

First of all, the TDS, hardness and pH values of the filling water should be taken into account. The pool water should then be tested and pH, alkalinity, calcium hardness and chlorine should be adjusted to target ranges. Especially if soft filling water is used, it should be ensured that the calcium hardness does not fall below the ideal range.

When establishing the balance after a water change, it is important to add chemicals gradually and distribute them under good circulation. It is necessary to verify the values by repeating the measurement after a while. It may take some time for the water to become clear and stabilize again. This process is actually part of regular water chemistry management. Water change should not be seen as a solution on its own, but as a complementary step of the correct maintenance routine. Our company helps you save water and achieve permanent balance by making your water change plan according to your pool volume and local water conditions.