Minerals and TDS
Mineral Staining
The use of sequestering agents becomes even more important in the control of stain producing minerals. Problems of stain formation on pool surfaces or colored water are most often associated with the metals iron, copper or manganese. Each of these metals can enter a pool by several means and will react in very different ways. One of the most common ways these metals can enter the pool is via the fill water. Therefore, before filling a pool, always be certain to have the water tested for all three metals in addition to the other chemical parameters. In this way you will be better prepared to deal with the initial pool treatment, both water balance and stain control.
IRON
Iron is the most common mineral found dissolved in water. It is colorless but will react almost instantly with chlorine or other oxidizers to produce a rusty red color in water, or worse, orange colored staining. As little as 0.1 ppm of iron is all that is needed to result in colored water and stains. The most common source of iron in pool water is the fill water. However, a simple water test does not always alert you to the possible presence of iron in the fill water. This is because over time, municipal drinking water piping systems gradually build up sediments in the pipes. This is not normally of great concern as the water flow is generally not sufficiently strong enough or of high enough volume to stir up these sediments into the flow of water itself. Often times when large quantities of water are drawn from municipal pipes, such as when a pool is first being filled, the heavy flow of water can cause ironbearing sediments laying in the pipes to be stirred up, causing them to enter your pool unexpectedly. If a test for the presence of iron were conducted prior to filling the pool, it would only identify iron if it were naturally occurring in the water. Any iron that may be in the sediments would likely be missed because the small amount of water drawn for the water sample would not be sufficient to stir up the sediments. Thus, the iron would remain in the pipes and not be detected until it was too late. The result could be a heavily stained pool that would then need to be emptied, cleaned or acid washed and refilled.
COPPER
A common cause of green water and stains ranging in color from blue-green to black is copper. Copper sources are more varied than iron. Copper can enter the pool water from corrosion in copper heaters, from some copper-based algaecides, and from the source water. Copper problems are often indicated by pool water with a true clear green color, whereas green water caused by algae would be green and cloudy.
Corrosion of gas or oil-fueled heaters that have copper coils results in copper entering the water flow, which, in turn, can lead to green water or stains. This type of corrosion is most commonly due to a chemical imbalance in the water such as low pH, low total alkalinity or low calcium hardness or a combination of these factors. A galvanic action can take place in heaters where the copper metal of the heater coil comes in contact with a different metal such as iron.
Copper algaecides are also implicated in causing stains in pools because of how the product was applied to the pool in the first place. Copper algaecides come in several types and some are more prone to staining than others. However, copper algaecides are usually very concentrated, requiring only a very few ounces to be applied for each 10,000 gallons of pool water. Often times, label directions are not followed and a significant overdose occurs. That is why it is important to follow the label directions. A safe product that will not stain is CLEAN&CLEAR by C-Pool Minerals. Copper can also come from the source water and will either be present as a normal component of the water or on a periodic basis. Many municipal water systems rely upon reservoirs for their water supply. These reservoirs frequently suffer from algae outbreaks and the algae is treated with copper. The copper level is often as much as 1.0 ppm, and if you fill or add water to your pool with this water, it will be green and could result in staining.
MANGANESE
Manganese will color the water from pink to deep purple depending on the level present. Manganese only enters the pool from the source water either through natural occurrence or after being intentionally added by a water treatment plant in the form of potassium permanganate ( as a iron removal chemical). The latter causes problems when it is inadvertently overdosed and then arrives at the pool when filling or adding water. Again, the biggest problem is that you simply do not know when the water may contain manganese. The important thing to understand is that all three metals can easily be kept from causing problems with the regular use of a sequestering agent.
As with calcium, the sequestering agent will chemically combine with the metals in the water and keep them from precipitating out of the water to cause staining. The best time to use a sequestering agent is when the pool is being filled for the first time, and thereafter as part of a regular preventive maintenance program. In this way, any metals that may be present in the fill water will be tied up or inactivated before they can cause a problem. Also, any metals that may find their way into the pool, either when water is added or from corrosive actions in the pool, will be prevented from causing staining. In other words, by adding the sequestering agent as part of the regular maintenance program, the pool will be protected from stains even when you did not expect metals to be present. It is far easier to prevent staining caused by metals than to remove the stains once they have formed.
TOTAL DISSOLVED SOLIDS
Total dissolved solids (TDS) are normally the least worrisome factor.TDS is the sum of all materials dissolved in the water and normally runs in the range of 250 ppm and higher. There is much discussion over what levels are considered too high, but there is no real lower limit. TDS is comprised of many different chemical compounds, which means that the issue of how much is too much actually depends more on what they consist of than how much there is. For example, sodium chloride or ordinary salt is extremely soluble and is therefore unlikely to cause a problem, whereas, as we have seen, calcium compounds can be a problem even at fairly low levels. In general, when the TDS exceeds approximately 1500 ppm, problems may begin to occur. It must be pointed out that pools whose sanitizing systems are based on chlorine or bromine generation equipment (salt generators) will likely have much higher TDS levels. These pools actually have salt in one form or another added to the pool. The salt used is highly soluble and does not cause the type of problems normally associated with high TDS, but never the less, it does add to the TDS level in the pool. When testing water in this type of pool for TDS, the salt intentionally added to the pool needs be taken into account. At elevated levels,TDS can lead to cloudy or hazy water, difficulty in maintaining water balance, reduction in sanitizer activity and foaming. Unfortunately, the only way to reduce TDS is to drain a portion of the water and replace it with fresh water. Sequestering agents do not help when high TDS levels are causing cloudy water.