Chemical Water Treatment for Cooling Towers
Chardon Laboratories is your best source for reliable cooling tower chemical treatment services. We will work with you to develop a customized cooling tower chemical treatment plan that will provide an effective defense against key contamination issues such as biological growth, concentrated mineral content and white rust formation. You’ll get the benefit of a guaranteed scale-free cooling tower water treatment system at a guaranteed annual price.
Cooling Tower Water Treatment
Cooling towers can range in size from fairly modest to extremely large, depending on the cooling loads of a facility. Chardon handles them all, and will tailor a maintenance program to meet your specifc needs.
Due to it’s exposure to the outside environment, the cooling tower is the primary source of contamination within your system. Acting as a large air washer, the “open” tower water loop accumulates airborne particulate and promotes biological growth. Through evaporation, it also concentrates mineral content.
Chardon utilizes a full line of corrosion and scale inhibitors, white rust preventatives, and microbiological inhibitors to create a custom chemical plan that addresses these problems and others to keep your cooling towers running efficiently.
“We don’t sell chemicals, we sell clean systems.”
Use these links to jump to the content you are most interested in:
- Cooling Tower Water Treatment Products
- Cooling Tower Water Treatment During Start-Up
- Cooling Tower Water Treatment for Heat Exchangers
- Cooling Tower Loop Water Treatment
- Refrigerant Loop Water Treatment
- Chilled Water Loop water Treatment
- Cooling Tower Start-Up Treatment Overview
- Cleaning Heat Exchangers Overview
- Preventing Corrosion and Fouling During Lay Up
- Controlling White Rust (Galvanic Corrosion) in Cooling Towers
- Reasons to Discharge Tower Bleed to Sanitary Sewers
- Controlling Aluminum Corrosion in Cooling Tower Systems
- Consequences of Low Flow in Cooling Towers
- Mass Balance & Cooling Tower Water Treatment
Overview of Our Cooling Tower Water Treatment Products
Our advanced cooling tower water treatment services include the precise utilization of our superior cooling tower inhibitor product line. We have developed products that are specifically designed to treat each specific condition that could lead to contamination.
For instance, some products will eliminate scale in cooling towers with hard, alkaline make-up water, while others will prevent corrosion in systems with soft or low TDS make-up water. Our well-trained, experienced ISO-certified technicians have the expertise to select and apply the right water treatment chemicals for your unique cooling tower maintenance requirements.
Effective Cooling Tower Water Treatment for New System Startup
The startup of a new cooling system is a critical period in its lifecycle. Chardon Labs offers cooling tower treatment for new systems with two clear objectives in mind: thorough cleaning and proper passivation.
During the equipment cleaning phase, we use cooling tower chemical treatment products that will remove in-transit oxidation, clean out corrosion by-products and eliminate oils and grease from manufacturer preparations. The goal is to ensure all system components are thoroughly flushed to prevent contamination.
Upon completion of the cleaning phase, the next step is passivation, which is a process designed to render component surfaces unreactive through the application of chemicals. There are different passivates designed for different cooling tower systems. Your Chardon Labs technician has the expertise to recommend the best cooling tower chemical treatment for your needs.
Our Cooling Tower Water Treatment Services Also Include Heat Exchangers
A cooling tower’s heat exchanger allows heat to flow through a material, usually a stainless steel plate or copper tube, from the hot side to the cool side. Scale, typically in the form of calcium carbonate, can accumulate on the surface of the exchanger and act as an insulator that reduces its efficiency.
Our water treatment chemicals are the most effective heat exchanger cleaning products currently on the market. We use advanced chemistry for the most effective cleaning. Corrosion inhibitors and dispersants ensure the metal is protected and post-cleaning fouling does not occur. Your Chardon Labs technician can also apply additional products for certain heat exchanger cleaning applications as needed.
Contact Our Cooling Tower Water Treatment Company to Learn More
Contact our cooling tower water treatment company for more information about these and other available cooling tower services.
Cooling Tower Loop Water Treatment
Water is carried from the condenser to the cooling tower, where it’s surface area is increased to facilitate evaporation. Some of the water is lost in the atmosphere, but the solids remain behind. When the cooled water reaches the sump, it is circulated back through the condenser, where it removes heat from the refrigerant.
Refrigerant Loop Water Treatment
The refrigerant is continuously cycled through the refrigerant loop. It absorbs heat from the chilled loop and is changed from a liquid to a gas in the evaporator. The compressor increases the pressure and temperature of the gas, which flows into the heat exchanger. There, the cooling tower water removes heat from the refrigerant causing it to condense back to a liquid.
Chilled Water Loop Water Treatment
The chilled loop is actually a closed loop where water is circulated throughout the entire facility continuously to fulfill the cooling requirements of the system.
Cooling Tower Services & Water Treatment
Overview of the Chardon Cooling Tower Inhibitor Product Line
What is the Chardon Cooling Tower Inhibitor Product Line?
Chardon cooling tower treatment utilizes a variety of cooling tower scale and corrosion inhibitors. Each product has attributed designed to address different conditions. Some products are designed to prevent scale in systems with extremely hard, alkaline make-up water. Others are designed to control corrosion in systems with very soft, or low TDS make-up water. No one product will address all conditions.
The Chardon Cooling Tower Inhibitor Line provides our Customers with the finest in chemical treatment products.
Is there anything special I need to know about using these products?
Only trained professionals such as your Chardon Service Technician should handle and apply water treatment products. Please use care in handling all chemical treatment products and always wear the recommended personal protective equipment. Refer to the SDS for complete safety and first aid precautions.
How do I test for these products in my cooling tower?
The steady refinement of testing methods has driven the development of new inhibitor products and in concert with proper product selection, accurate testing is the key to performance. Most Chardon inhibitor products are designed to operate at 50 ppm. The Chardon Inhibitor Formula is the right place to start when setting up a new chemical feed program. Once the cooling tower has cycled up and reached equilibrium, we test the concentration of the tracer identified.
Start-Up of Cooling Towers – Cooling Tower Water Treatment
Cooling Tower Start-Up Overview:
The startup of a new system is an important time in the life cycle of a system. Chardon Laboratories understands that it is vitally important to properly clean and passivate the systems to ensure excellent protection, long life, and proper operation of the equipment.
The procedures themselves are straightforward, the challenge comes from the ability to implement them at the proper time and the proper order. New construction sites have many different demands and timetables than a far simpler equipment upgrade job. Depending on the site timetable loops may start before condenser systems, condenser systems may start without chillers in place yet, systems may start up, then sit idly afterward for periods of time until actually running with load, different manufacturers may have different recommended procedures or none at all.
Chardon is able to address these issues and make overall recommendations for the best way to properly passivate and protect systems under these and other varying conditions.
Cooling Tower Water Treatment at Start Up General Overview:
Chardon has two major goals in startup chemical treatment. The first is to clean the systems. The metals in the components develop corrosion by-products during shipping and installation. Despite the manufacturers best efforts to protect the components during this time period, some oxidation and corrosion occur. Some of the protection methods actually introduce materials that need to be removed before operation.
A specific example would be the oil coating on new steel pipe. Debris is also introduced into the components during actual construction. The second goal is to passivate the various metal surfaces to minimize future corrosion. Let’s look at each of these in further detail.
Cooling Tower Water Treatment & Cleaning:
Chardon’s first step is to clean the equipment. We add chemical products to the system that are designed to remove in transit oxidation, clean out corrosion by-products, and clean out oils and grease from manufacturer preparations. We also add biocides that will kill any micro-organisms that may be in the components already.
During this phase, the systems are filled with water and then circulated with water and the chemicals through the entire system for at least 48 hours to ensure a thorough cleaning of all components. At the end of that time, the system needs to be thoroughly flushed until the water in the system is clean. The best method is to open low point drains throughout the system to flush any heavy debris out, then leave open low point drains sufficient to purge the system without overrunning the makeup capability of the system.
The system pumps should be left running at this point to circulate water through the system yet. It is best to flush the system in this manner to get a good removal of all debris. When the system has turned over approximately five times the volume and the water tests out clean any start up strainers should then be removed and cooling towers should be drained and washed out.
The key to all of this is to make sure that ALL the system components get flushed. If this is not possible due to timetable constraints, then the equipment that does not receive a flush must be flushed separately prior to coming online to prevent possible contamination of already cleaned components.
Passivation in Cooling Towers:
The next step is passivation. Condenser water components are already passivated from the cleaning chemical, with the possible exception of the tower. There are different treatments for different systems, and your Chardon Representative will determine the proper one. The important thing is to add them in right away, and circulate them throughout the entire system. The sooner they go in after flushing the better.
Cooling towers may require additional special chemical treatment for a longer period if they have galvanized components. The galvanizing requires extended passivation to prevent the formation of white rust.
Cleaning Condenser Systems/Towers:
These components are cleaned and passivated at the same time by the addition of Chardon’s recommended chemicals and biocides. As mentioned before, they should be circulated for at least 48 hours, then flushed. Again, it is critical to make sure that ALL the components get this treatment.
Open all valves and zones to ensure complete circulation. Any and all chillers, towers, pumps and piping need to have circulation through them. If for some reason, not all components can be flushed at this time, they should be flushed separately before being put online. The towers should be drained and washed out after the flush, and start up strainers removed. The flush is done when phosphate and iron levels in the water approach 0.3 ppm or less and the conductivity of the flush water equals that of the make-up water.
If the towers have galvanized components, the necessary treatment must be in place to begin treating for white rust upon completion of the flush.
Cleaning Heat Exchangers
Where Does Scale Come From in Heat Exchangers?
Scale comes in a variety of forms, but the most common is calcium carbonate, or CaCO3. Calcium scale precipitates when the threshold solubility of calcium and carbonate is exceeded. Calcium and alkalinity exist in different concentrations in virtually all make-up sources. As evaporation removes pure water from the cooling tower, the dissolved solids remaining increase in concentration. If the concentration becomes too great, the combine to form calcium carbonate scale.
How Is This Usually Controlled?
Preventing scale formation is a combination of controlling cycles of concentration and modifying the solubility of calcium carbonate with chemical threshold inhibitors or other means. By knowing the threshold solubility, or the concentration at which scale begins to form, we can control the conditions at a safe margin below this point. This is a fundamental principle of cooling tower treatment.
How Do I know If Cleaning is Necessary?
Heat exchangers allow heat to flow through a material, generally a copper tube or stainless steel plate, from the hot side to the cool side. Scale or any other material that accumulates on the heat exchange surface acts as an insulator and reduces the efficiency of the heat exchanger. Most heat exchangers are designed to operate at a specific temperature range called ΔT (Delta T). The ΔT describes the difference between the temperature going into and coming out of the heat exchanger. A reduction in the ΔT is an indication of a reduction in heat transfer efficiency. This is typically due to scale formation, microbiological fouling or mud settling in or on the tubes.
Which Product Does Chardon Use For The Cleaning?
Chardon Scalzo is the most effective product for cleaning heat exchangers, although some require special products. Scalzo contains chemistry for the most effective cleaning, plus corrosion inhibitors and dispersants to ensure the metal is protected and post-cleaning fouling does not occur. Scalzo is not recommended for some materials, stainless steel in particular. Please consult your Chardon Representative of chemical recommendations.
Preventing Corrosion and Fouling During Lay Up
Why Does Chardon’s Cooling Tower Treatment Program Stress The Importance of Laying Up Cooling Towers?
If left to grow unchecked, the bacteria that live in your cooling tower will colonize pipe and other wetted surfaces. Over time these colonies will grow into thick biofilms that reduce heat transfer, prevent corrosion inhibition strategies, and even cause corrosion.
Cooling tower water commonly supports large populations of bacteria and algae. Air pulled through the tower contains particulates and those particulates harbor microbes. The cooling tower scrubs the particulates out of the air and the water offers the microbes a place to grow and multiply. The water may look clear, but microbe counts as high as one million or more cells per milliliter can thrive in cooling tower water. That’s up to a trillion bacteria in 1,000 gallons of tower water!
How Much Bacteria Is Too Much Bacteria In My Cooling Tower?
The Cooling Tower Institute, ASHRAE, Chardon and other professional organizations have identified a population level of 105 cfu/ml* or lower as efficient. Bacteria are over 98% water and do not impact evaporation or heat transfer as free-floating cells. When the population exceeds the carrying capacity of the environment, bacteria secrete a coat of extracellular polymer, better known as slime.
This slime traps other particulates, harbors both living and dead bacteria, and eventually grows into a complex community knows as biofilm. Biofilm has an insulating effect on heat transfer, can clog piping and reduce flow rates, and can promote corrosion beneath the biofilm by a variety of mechanisms. If left to grow out of control, biofilm will support rich, complex communities that may include multicellular organisms such as rotifers and roundworms.
What Are The Problems With Biofilm In My System?
Biofilm forms a boundary between the water and the copper and steel in your tower and heat exchangers. Chardon has found that this boundary reduces heat transfer efficiency. In fact, biofilm creates even more heat transfer problems than calcium scale. Biofilm also prevents corrosion inhibitors from reaching the base metal. Biofilm can harbor Legionella and other potentially harmful species.
Microbiologically influenced corrosion, or MIC, can occur within biofilm and attack tube sheets, end bells, and other system components that are protected during normal tower operation. Biofilm also supports under-deposit corrosion that can weaken metal components and shorten equipment life.
What About Algae In My Cooling Tower?
Chardon knows that algae can be a problem in cooling towers where a significant amount of sunlight reaches the water. Much like bacteria though, a little algae in the sunlit parts of a cooling tower does not reduce evaporation or heat transfer. Thick mats of algae can promote under-deposit corrosion and harbor other damaging bacteria. Long strands of algae that break free can clog strainers or other fine orifices in your system.
Algae dies quickly once it breaks free of its hold in the sun and flows into the darkness of a piping system. Dead algae decomposes and can provide nutrients for bacterial communities, but the main impact of algae is the clogging of intake screens and other strainers in the system.
How Can I Prevent Biofilm In My System?
One of the goals of Chardon’s cooling tower treatment program is to manage the population of bacteria at or below the recommended level of 105 cfu/ml. Most bacteria are not inherently harmful, but bad things can happen when they grow out of control. It is important to realize that we encounter these bacteria every day when breathing the air around us, touching countertops or sinks, or working in dirty areas. There are no dangers at very low exposure levels.
Keeping bacteria populations at or below the 105 cfu/ml level will prevent biofilm formation. Chardon chemical treatment programs use biocides to control bacteria.
What Happens When My System Is Offline?
Your equipment is protected by Chardon’s cooling tower treatment while it is online and operating, but what about during short-term shutdowns or the offseason? Bacteria grow exponentially; that is, one cell divides to form two cells, those two divide to form four, then eight, then sixteen, and so on. If left unchecked, bacteria will multiply and begin forming biofilm.
What Can I Do To Prevent Biofilm When My System Is Offline?
Following an accepted layup procedure is the best practice. Chardon’s best practice for protecting systems during seasonal or long-term layup is to drain condensers and heat exchangers as soon after shut down as possible. Microbiological fouling can proceed quickly and the cleaning and inspection will be easier when performed soon after shut down.
First cycle the system down to help flush out particulates, then circulate a product such as Chardon’s CT Lay-up. An airtight desiccant layup program should be considered for longer periods of inactivity.
What If I CAN’T Drain My System?
Cooling tower systems that operate intermittently during the cooler months will have biofilm problems and the problems could be severe if operation only occurs for a few hours a week. Chardon cooling tower chemical treatment products can remain active in the system even when it is not circulating, but all biocides have a certain half-life and protection rarely lasts more than a couple days.
Serious consideration should be given to isolating secondary components and draining them per the outline above. If draining is not possible, program the energy management system to circulate water through offline components twice daily in coordination with the biocide to help prevent biofilm formation.
Controlling White Rust (Galvanic Corrosion) in Cooling Towers
What is White Rust? Why Is There White Rust In My Cooling Tower?
White rust is a white, waxy material that can accumulate on the galvanized surfaces of newer cooling towers. Galvanized sheet metal naturally passivates with a protective layer of zinc oxide. Chemically this passivation layer is a combination of zinc hydroxide and zinc carbonate. It is important to control white rust immediately or more extensive and damaging corrosion will occur. White rust forms when galvanized steel is exposed to water with excess carbonate ions and a pH above 8.3.
When Did This Problem Arise?
Metal was traditionally galvanized using a “wet” dip method that promoted the development of the beneficial zinc oxide passivation layer. New “dry” galvanizing methods were employed by tower manufacturers in the late 1980s which involve more aluminum in the process have made the formation of white rust more likely.
What Can Be Done About White Rust In Cooling Towers?
New galvanized cooling towers should be treated to maintain the pH of the circulating water below 8.3 for a period of six to nine months. This will ensure that the alkalinity of the tower water remains below the level at which white rust forms. Under these conditions, galvanized surfaces form a protective layer of zinc carbonate which helps protect the steel beneath the galvanizing.
Also, the combination of low ph and phosphate-based chemicals can significantly reduce the time needed to properly condition a new cooling tower (30 to 60 days depending on water
conditions). The use of Chardon’s chemistry inhibits the production of excessive levels of zinc carbonate, allowing the natural oxide layer to form providing long-term protection.
What Chardon Will Do to Control White Rust In Your Cooling Towers
Depending on the chemical characteristics of your make-up water, your Chardon Service Technician will adjust the controller to operate the system at lower cycles of concentration and therefore lower pH. This option will result in a significant increase in water consumption during the passivation period.
The alternative is to install an extra chemical pump which will periodically administer a solution of sulfuric acid to maintain the pH of the tower water below 8.3. The sulfuric acid reacts with and neutralizes the natural alkalinity in the cooling tower water producing only natural by-products.
After the six to nine month treatment period, your Chardon Representative will be able to return your water treatment program to its normal operating routine.
Alternatively, adjusting the system to lower cycles of concentration and maintaining lower ph, the use of acid can be eliminated and replace it with the appropriate phosphate product. Maintaining a level of 300-400 ppm as PO4 for 30-60 days in the presence of 200-300 ppm of calcium hardness will allow the galvanized metal to properly passivate.
Good Reasons To Discharge Tower Bleed to Sanitary Sewers
Cooling tower treatment requires the controlled discharge from cooling towers and other recirculating water systems is designed to maintain a certain level of water usage efficiency, or cycles of concentration. Evaporation causes the concentration of naturally occurring dissolved solids in cooling tower water to be greater than the water source from which it started.
The scrubbing effect water has on air pulled through the cooling tower to increase evaporation causes common, naturally occurring bacteria to become more concentrated in cooling tower water. The safest and most environmentally responsible way to get rid of the controlled discharge of cooling tower water is to drain it to the sanitary sewer.
Unfortunately, many older systems were designed to drain cooling tower water directly to drainage tile fields, collection ponds, ditches, creeks or other storm sewers. In 1987 the Environmental Protection Agency (EPA) enacted the Clean Water Act. With it came the need for a permit under a process called National Pollution Discharge Elimination System, or NPDES. The intent of this process is to restrict and eventually eliminate the discharge of “pollutants” to storm sewers and other surface water sources.
NPDES has proven to be a significant expense to many companies with cooling towers. There are only two options: discharge tower water to a sanitary sewer to sewage treatment facility, or obtain an NPDES permit. If cooling tower water is not already discharged to a sanitary sewer, then plumbing the discharge to an acceptable sewer is usually the best option. Only as a last resort should an NPDES permit be pursued.
For 2000, the EPA has enacted several important changes to their NPDES program. Most are designed to tighten the requirements and make it more difficult for companies to obtain this EPA permit. Here is a synopsis of the changes.
Your Chardon representative will be glad to discuss these and other details of the NPDES program with you at your convenience. If you have any additional questions, please feel free to contact the Chardon Technical Support Staff.
Controlling Aluminum Corrosion in Cooling Tower Systems
What Is The Problem With Aluminum Corrosion in Cooling Towers?
Aluminum is lightweight, easy to tool and has been used in many industries for years. Unfortunately, aluminum has different solubility and corrosion resistance characteristics than most materials common to cooling towers and recirculating water systems.
Most water treatment strategies are designed to address corrosion and scaling concerns on a variety of materials, but water chemistry that protects metals like steel and copper can present an aggressive situation on aluminum. Aluminum is a very stable metal in dry air, but aluminum components treated by recirculating water systems is another matter.
What Is The Solution for Aluminum Corrosion In Cooling Towers?
The corrosion rate of aluminum increases when the pH of the water exceeds 8.0 and becomes severe when the pH exceeds 8.4. A treatment program designed to protect aluminum components should maintain the pH of the water between 7.5 and 8.0. Unfortunately, this has an adverse effect on ferrous metals in the system.
The corrosion rate of iron is elevated significantly in this neutral pH range. One must carefully weigh the benefits of a neutral pH program for systems constructed primarily of ferrous metals against the cost of replacing aluminum components with plastic or brass pieces.
When the cost favors a neutral pH program designed to protect expensive aluminum components such a mold(s), the acid must be used to maintain the pH of the water within the 7.5 – 8.0 range. Chardon cooling tower treatment may feed using the inhibitor relay, although a controller capable of controlling based on pH offers the most reliable solution. For systems with accurate pH control, we will offer a specialized corrosion protection program and maintain the feed rate between 1.0 and 1.5 ppm as zinc.
Systems with softened make-up present an additional problem. The combination of low calcium hardness and low pH can significantly accelerate corrosion on ferrous metals. To prevent this combination from corroding the system, soft water can be blended with unsoftened water to deliver approximately 100 ppm of calcium hardness in the system water.
What About Automotive Antifreeze For Aluminum Engine Blocks?
Silicate-based corrosion inhibitors will form passivation films on aluminum and reduce corrosion, but these products also form silica scale on heat exchangers. The effect of silica scale on heat transfer is nine times as great as calcium scale and this technology is rarely used in industrial applications.
Consequences of Low Flow in Cooling Towers
What Is Low Flow In Cooling Towers?
A cooling tower is designed to remove heat by evaporation of water. The tower is also designed to have a minimum and maximum amount of water flow over (or through) the tower’s “fill”. The fill in the tower is designed to increase the surface area of the water that can be exposed to air. The larger the surface area of the water passing through the fill, the more efficient and faster the heat transfer to the atmosphere.
When the amount of water passing through the tower fill is less than the designed minimum amount, it is considered “low flow”.
Why Is Low Flow In Cooling Towers A Problem?
Chardon understands that during normal operation of a cooling tower, the required evaporation will increase the concentration of the dissolved solids. Therefore, the hot water at the top of the tower will increase in dissolved solids during the evaporation process until it hits the bulk water in the sump of the tower. When the normal amount of water is passing through the fill, the resulting concentration of dissolved solids in the sump is usually negligible during a single pass.
However, when less than the minimum amount of water is passing through the fill, the evaporation process will still remove the same amount of water from that low flow. The concentration of the dissolved solids in the low flow water will increase much faster. It may increase so rapidly that the current cooling tower treatment chemicals in the water may not be able to keep the dissolved solids dissolved any longer and some precipitation may occur!
How Do I Know When There Is Low Flow In My Cooling Tower?
By inspection of the tower, normally the “hot decks” (or distribution pans) are supposed to be filled to about one inch from the top of the pan. If you observe that the water level in the hot deck is much less than one inch from the top of the pan, then you may have the problems mentioned above. Typical towers usually have about 4 to 6 inches of water depth in the hot deck. If the fan on the tower is running and you have low flow, then the problem of over-concentration of dissolved solids is going to be more severe.
How Do I Correct Low Flow In My Cooling Tower?
You should verify from the tower manufacturer the amount of designed water flow for that individual tower. The tower manufacturer may need to know the orifice number to determine the normal water depth in the hot deck. If the water in the hot deck does not approach the estimate of the tower manufacturer, then notify the person responsible for the facility of your findings.
Some possible solutions are: open the balancing valves further, clean pump strainers, check valves that limit flow to the tower, clean rust chips from the balancing valves, etc.
Mass Balance & Cooling Tower Water Treatment
What Is Mass Balance & Why Is It Important to My Cooling Tower Treatment Program?
Mass balance is a relationship between the amount of chloride ions and the amount of calcium ions in solution. The chloride ion is very soluble and will not precipitate even at extreme cooling tower conditions. Under certain conditions, the calcium ion will precipitate out of solution and form calcium scale.
By comparing the relative amounts of these two ions in solution, one can determine whether scale is accumulating or being removed. Chardon is one of very few companies that understands the importance of this metric.
How Mass Balance Work In Cooling Towers
Cycles of concentration is typically calculated by dividing the concentration of chlorides in the tower water by the concentration of chlorides in the make-up water. The same concept of cycles can be applied to calcium hardness: divide the calcium hardness of the tower water by the calcium hardness of the make-up water.
Mass balance is calculated by subtracting the value for chlorides from the value for calcium hardness, or MB = CaH – Cl-.
What Does Mass Balance Work In Cooling Towers?
Positive mass balance values indicate that there is more calcium in solution than would be predicted by simply cycling up. Typically, surplus calcium comes from dissolving deposits in the tower sump or on fill slats.
Negative values indicate a loss of calcium relative to the amount that there should be at the current number of cycles of concentration. This is an indication that calcium is precipitating out of solution and building scale on heat exchange surfaces.