Metals are naturally existing elements found in every place; in water, soil and stones. Metals in soil and stones dissolve in acidic rainwater, which is then carried to surface water and groundwater. Through this, the dissolved metals find their way to pools and tubs when filled. Exposure of metals to water cause staining on pool surfaces and equipment. This article discusses the techniques to control the presence of pool metals. It also discusses the different kinds of metal staining and the relevant chemicals to eliminate and hinder stains.

Metals in pools and hot tub water

There are 91 existing metals, but only 6 are problematic to hot tubs and pools. The 6 metals include magnesium, copper, cobalt, iron, manganese and calcium. Here we will only discuss 4 that are cobalt, copper, magnesium and iron.

Fill water, inclusive of almost all municipal and well water supplies that fill hot tubs and pools, contains a few metals. It is advisable to test for metal concentration in source water before filling the hot tubs and pools.

Tests for iron and copper are easily accessible, though the majority only measures the free form of the dissolved metals. They also do not test the sequestered and complexed forms of dissolved metals. A two-phase metal test containing adequate reducing and releasing agents give better results on free, complexed and some oxidized metals.

Sources of metal contamination in the pool and hot tub water are plaster and pebble surfaces, water features, decking materials, metal equipment, galvanic corrosion, chemicals and runoff.

In addition, flagstone, marble and stone contain iron that leaches into the pool after every rainfall. Imbalanced water may cause the introduction of copper from heat exchangers found in gas-fired water heaters. Moreover, copper-based algaecides and mineral-based water treatment may be a source of pool metals. Plant fertilizers can also introduce metals when incorrectly applied or due to uncontrolled flooding. More sources of metal include irrigation methods with well water.

Preventing stains

Water Treatment

Avoid using untreated water with high metal concentration (higher than 1ppm) in hot tubs or pool. Treat the water when the metal concentration is higher than 0.2 ppm. Sediment filters (10 microns or less) eliminate the majority of the bigger oxidized particles. Use filters that have metal adsorbents to treat water, to minimize dissolved metals concentration.

Primary Sanitizers and Stabilizers

Maintain proper concentration of primary sanitizers and other similar stabilizers to prevent organic contaminants. These include; pathogens, non-hazardous bacteria and algae minimizing the need for a copper-based algaecide.

Bonding of Metals and Water

The majority of the pool and hot tub equipment are metal-made. For example, electrolytic halogen generators, the heating core of electric heat pump, gas-fired pool and hot tub heaters, ladders, light rings and handrails.

To enhance chemical and electrical safety, install a bonding system in the hot tub or pool. The bonding system involves joining the copper wire with all the metal elements and water combined. This minimizes electric potential difference. Lack of this system, enables dissolution of pool metals, causing staining that damages the equipment. This is the process known as galvanic corrosion and can heighten due to several factors such as salt water, stray direct current as well as its power supplies. Anodes (zinc metal) reduce the damage on the equipment but don’t deal with the cause of corrosion. Test the bonding system every year, or any other time there is corrosion.

Pool & Hot Tub pH

pH is the most vital yet most ignored factor in preventing metal release in water. Low pH water (below 7) is acidic and corrosive. Acidic water dissolves metals from the pool equipment.

Improper water chemistry harms pool surfaces and machinery. Always ensure to maintain an accurate pH, alkalinity (carbonate) and calcium (hardness). If inadequate, water draws carbonate and calcium from cementitious surfaces, discharging metals into the water.

Sequestering Agents

Sequestering agents join with the dissolved pool metals to reduce oxidation hence reduces staining. They chelate the metals, not eliminate them. They require a complex modern ultra filtration system to remove sequestered metal particles as the particles are too small for the pool filtration system. Add this agent on a regular basis, as a secondary disinfection and primary sanitizer systems keep on destroying them.

Ways to reduce metal concentration in hot tubs and pool water

• Bind the metals using polymer and water-insoluble natural adsorbents
• Filter the water through a reverse osmosis system
• Remove and replace a part of the water with fresh metal-free water

Removing stains from the pool and hot tub surfaces

1. Metal stain removal from the surface

2. Chelation of the dissolved metals in the water with a sequestering agent

3. Elimination of the metals from the water.

To get rid of pool metals and metal stains, add oxalic acid, ascorbic acid and citric acid or a similar product into the pool water. An experienced pool service expert should only execute the use of Muriatic acid in the removal of metal stains as it can lead to permanent damage to the pool surface. Chelation of dissolved metals and minimizing concentrations of dissolved metal have been earlier tackled.

Figuring out the difference between metal stains and those by organic contamination can be difficult. For evaluation, establish the origin of the stain, asses the water chemistry and test the stain with either citric acid or ascorbic acid.

Note: Some organic stains, similar to those brought about by iron bacteria, vanish after treatment with ascorbic acid but return with the introduction of chlorine residuals.

Several ways are applicable when heating water in a hot tub. These include; the use of electricity, solar, heat pumps, and external heat change. Looking at it from a narrow perspective, it is practical to use electricity to heat portable hot tubs. With this, there is no need to consider other alternatives. From a broader perspective, when it comes to inbuilt concrete tubs, common in health spas and resorts, the situation is different. It holds large volumes of water, meaning it is uneconomical and impractical to heat the water using electricity. This paves the way for the use of fossils fuels, which are an alternative source.  

The dominance of electric heaters

Electric heaters are convenient and dominant with portable tubs. Brian Koops, Vice President of Engineering and Technical Services for Jacuzzi, states that all his company vessels use electricity. This is because it is reliable and compact, hence placed in a central cabinet. Only one heater is necessary to run all the machines in the spa.

 John Milligan, CEO of NESPA, a manufacturer of prefabricated custom spas, agrees with this notion. Electric heaters are preferable because they are clean, easy to use, and maintain. Electricity eases so many technical parts of life. In the same way, electric heaters speed up the manufacturing and installation processes. In case of a fault, all that’s required is a replacement. All operations are back to normal in minutes. When it comes to other sources of energy, they do not bear the same benefits.

Professionals in the spa industry don’t dispute the benefits brought by electric heaters. They believe that more focus should be on improving existing electric heaters. The same old models of heaters have been in place for a long time, and engineers should consider improving the standards. The material used to make the heaters is prone to corrosion, giving users a hard time dealing with it. The use of friendly material is preferable in the evolvement of the heaters.

System effectiveness

As stated earlier, electric heaters heat water fast, though it’s indisputable that gas heaters are faster. Approximately, in an hour, electric heaters raise the temperature of water by 4-6 degrees Celsius. This is in consideration of the volume of water and the size of the heaters.

The main concern is how effective the electric heater is in meeting the needs of the client. Hales states that to increase the temperature of the water that is 60 degrees to 100 degrees by evening, it will require the use of different heaters or a different way to operate the system to maintain the high temperature. Clients choose how they want to operate their spas. They can use the five and a half kilowatts heaters that are really fast but costly. They can also opt for a 4 kilowatt, which is slow and maintains temperatures at a certain level without using excess energy.

California Energy Commission dictates the energy consumption and standard efficiency in portable spas. They require spas in the Golden States to meet the set requirements for yearly energy consumption. These standards are not compulsory, but if one wishes to sell these services within California, they will be bound by this law. This statute has been adopted by other states as well.

Koops, states that the systems are made in a way that it is directly connected to water so that all the energy passes to the water. This, however, does not guarantee 100% effectiveness. It is possible to lose heat from the water. When the electrodes are transferred to water, energy has no other place to go; therefore, heat is lost to the atmosphere. Due to this, usage and maintenance of water is part of the system efficiency. Managing the systems so that there is no heat loss is a huge challenge to the constructors. Hales explains that foam insulators are useful in coating heaters to prevent heat loss, exempting the area in contact with water. 

The area of the hose is also foam-coated instead of the use of pipes to prevent the cooling of water.

Hydraulic efficiency is also important to improve the general efficiency of the spa. This gives way for a smooth flow of water delivered to consumers for therapy. These are just a few ways to improve spa Efficiency. Constructors have to look into the functioning of the whole spa systems and energy efficiency as well as to update these areas.

Usage of high efficiency insulated cover, insulation in the cabinets, and on-board software all play an important part in improving spa efficiency.

Determining the energy source

Milligan prefers the use of both gas and electricity for his prefabricated custom spas, which are bigger than portable spas. Consumers don’t necessarily know exactly how hot tubs work, but they purchase these vessels with expectations. It is important to explain to clients clearly when choosing the type of energy source required. The cost, the temperature desired, how to get to the desired temperature, and maintenance are factors to consider.

If you want your water to heat faster, the gas would be a better option. If you wouldn’t mind waiting for the water to heat and maintained at that temperature, then electric energy will be appropriate. The cost depends on the cost of the energy source chosen. Insulation is also a factor when choosing the type of energy. It is mandatory for vessel insulation when using electric energy. The issue arises when the vessel is more than 100 inches wide. Subtract 5 inches on each side to sit on, 90 inches remain. If the vessels are bigger than this, there is no other alternative than to switch to gas energy. It is a common problem in freeform vessels, and opting for rectilinear is a convenient design. At the end of the day, these factors are important for customer satisfaction.