How to remove metals from pool & spa water
"How do I get iron out of my pool water?"
Frequently as pool and spa retailers we encounter customers who are dealing with water with high mineral content. Usually the minerals are calcium, copper, iron or manganese. Customers often describe water that was one moment crystal clear and the next green, purple or reddish brown.
Minerals can become a problem in the water when they are oxidized by chlorine, bromine or less frequently by hydrogen peroxide. The afore mentioned are commonly used pool and spa sanitizers because of their abilities to release massive amounts of oxygen when they come in contact with water, thus killing bacteria by essentially smothering them.
When the minerals come in contact with oxidizing agents they react by quickly changing color, causing staining on most surfaces with which they contact.
While the staining is harmless, it’s quite unsightly on the surface of an investment that likely cost thousands of dollars and can require many hours of labor to remove.
In dealing with this problem, science is our friend. If we understand why the staining has occurred, we can determine the best method of rectifying the situation and avoiding it in the future.
First we need to identify the problem. It’s unlikely this type of mineral problem occurs overnight. That is not to say that mineral content in a water source can’t change over time, because it can and does.
Several years ago we witnessed what happens when a lengthy drought is followed by consistently large amounts of precipitation.
At the time I was managing our Brooklyn Park location. The municipality derives its water from wells as opposed to several others near it. Several neighboring communities purchase their water from Minneapolis which treats Mississippi river water for its residents and then in turn sells the surplus to them.
The drought ended at the end of pool season and was followed by a series of downpours in the fall. As spa owners refilled their spas one last time before winter set in, they noticed that when they shocked the water for the first time that it turned almost immediately to the color of tea.
When the rainwater ran down into the water table, it brought with it iron trapped in the soil, turning a mild problem into serious irritation.
When Brooklyn Park’s neighbor Minneapolis finishes the treatment process, their water has been “softened” and staining is no longer an issue for their end-users.
The situation is different for communities like Brooklyn Park where end-users must do their own treatment to eliminate the mineral problem.
For new pool and spa owners it’s advisable to find out prior to filling the pool or spa, what water conditions they will be dealing with for the foreseeable future.
Iron and manganese are minerals that won’t harm you, but they may cause reddish-brown or black stains on swim suits, ladders and most pool or spa surfaces. Under Environmental Protection Agency (EPA) guidelines, iron and manganese are considered secondary contaminants. Secondary standards apply to substances in water that cause offensive taste, odor, color, corrosion, foaming, or staining but have no direct affect on health.
Normally, water appears clear when first drawn from the cold water faucet. If not, it may contain ferric iron or organic iron; both color the water. Ferric iron precipitates or settles out, but organic iron won’t. In well water, insoluble iron oxide is converted to a soluble form of ferrous (dissolved) iron. Ferrous iron is colorless, but when in contact with air, it oxidizes readily, creating reddish- brown, solid particles that then settle out as ferric oxide.
Manganese is less common than iron in groundwater. It’s rarely found alone in a water source, and generally found with dissolved iron. Manganese is similar to iron but forms a brownish-black precipitate and stains.
As water moves through soil and rock, it dissolves very small amounts of minerals and holds them in solution. Calcium and magnesium dissolved in water are the two most common minerals that make water “hard.”
Water softeners can remove small amounts of minerals. Water is flushed from the softener medium by forcing sodium-rich water back through the unit. This method is impractical when filling a vessel as large as a pool and also creates other problems. Soft water will leach minerals from wherever it can be found in the sealed system. So if soft water is used, calcium chloride should be added to the water to avoid the pitting of pool or spa heater elements. The ideal range is widely considered to be 250 to 500 ppm of hardness.
Dissolved minerals are easily oxidized to a solid form by mixing water with air. A pressure aerator mixes air with the water, the air is vented, and then the solid particles are filtered from the water, adding no chemicals to the water. The filter must be backwashed or purged frequently to properly maintain the system. To protect the water from bacterial contamination from the air, the system should be totally enclosed and only potable water should be used. When using this method appropriate pumping capacity must be maintained for adequate air intake. Pressure aeration would likely be installed to serve a dual purpose for the homeowner, primarily for drinking water, bathing, laundry, etc.
When the concentration of minerals is not very high, an oxidizing filter using natural manganese greensand can be used. Manganese Greensand is capable of reducing iron, manganese and hydrogen sulfide from water through oxidation and filtration and has been used in the U.S. since the 1950's for this purpose. They usually range from around $500 to $1500.
When the mineral content is above 10 ppm, a combination of chemical treatment and filtration could be necessary. Small chemical pumps are used to add chlorine bleach, potassium permanganate, or hydrogen peroxide into the water. After a retention time of at least 20 minutes to allow for oxidation of ferrous iron into the insoluble ferric form, the solid particles are filtered out. This isn’t very practical for pools that can hold tens of thousands of gallons.
Complexation is a chemical reaction that takes place between a metal ion and a molecular or ionic entity known as a ligand that contains at least one atom with an unshared pair of electrons. In plain English, it’s a simple and low cost method for removing minerals from water. A phosphate compound or sequestering agent is added to the water to tie up or complex the dissolved minerals. This can be the most economical solution to the problem.
The downside to using phosphates in pool water is that algae only require amounts measured in ppb for reproduction. Without sufficient phosphates, algae soon die off. There are phosphate “sponges” that draw them out of the water, but this simply adds to the cost, making complexation less practical.
There are many complexation products on the market that utilize phosphoric & phosphonic acid, so I won’t bother listing them. However, SeaKlear manufactures a product called Metal Klear, a non-phosphate based metal stain control product, great for use in salt-water generator systems or areas with high phosphates. Before adding any oxidizer, simply add 1 quart per 10,000 gallons. Dilute in a pail of water and add to the deep end with the pool’s circulation pump on. For freshly stained pools or discoloration of water from metals, add 2 quarts per 10,000 gallons. As a maintenance dose, add 6-8 ounces per 10,000 gallons added to deep end weekly.
Mechanical filters are yet another commonly used methods to filter minerals out of water. There are numerous choices to pick from and for many years we’ve carried Hayward’s Bobby. Bobby is a hose-end attachment that filters down to 5 microns and can be reused until it no longer filters properly.
New to our stores for the 2013 season, Pentair Water’s Standard Filter Housing is manufactured of a durable polypropylene or clear FDA-compliant Styrene-Acrylonitrile (SAN) and equipped with 3/4" NPT inlet and outlet ports that fit most garden hoses. Standard Filter Housing is available in both 20" length and will accommodate a wide range of 2-1/2" to 2-7/8" diameter cartridges. The reinforced polypropylene cap offers an optional pressure relief button on the inlet side to relieve pressure inside the housing when changing filter cartridges.
Pentair Water’s Standard Filter Housing can either be used as a hose-end attachment or plumbed in as an in-line filter on a designated line for start-ups and refills.
Reinforced polypropylene housings have excellent chemical resistance and are ideal for many residential, commercial and industrial applications and are sold with Hydro-Cure® sediment cartridges.
As a depth filter, Hydro-Cure® sediment cartridges trap particles throughout the entire cross-section of the filter. Larger particles are trapped on or near the surface of the filter and the smaller particles are trapped throughout the inner layers of the cartridge. The gradient density design allows for optimum dirt holding capacity and minimal change-outs.
Hydro-Cure® melt blown filter cartridges are made of polypropylene resin meeting FDA regulation 21CFR177.1520. No binders, lubricants or antistatic agents are used in the manufacturing process. Clack melt blown polypropylene filters have been tested and certified under NSF/ANSI Standard 42 for material requirements only. The inert polypropylene resin provides exceptional chemical compatibility to handle a wide range of process fluids.
Hydro-Cure® cartridges are designed for knife edge seal housings to provide a positive seal without the use of end caps or gaskets. Hydro-Cure® cartridges are interchangeable with most standard pleated, string wound and other melt blown cartridges.
Hydro-Cure® melt blown polypropylene filters are designed for sediment reduction from potable water. These filters will not remove cysts, bacteria or viruses. Hydro-Cure® cartridges are designed to provide high flow rates with minimum pressure drop. Flow rates of up to 5 gpm per 10” length are recommended and should not exceed 10 gpm per 10” length for optimal efficiency. The maximum operating temperature is 125°F.
Hydro-Cure® filters are available in 1, 5, 25 and 50 micron ratings; we only carry the 1 micron rated version in 20” length. Cartridges are individually shrink-wrapped and labeled. Hydro-Cure® sediment filters have the micron rating embossed on the side of every cartridge for easy identification.
The initial set-up cost of $120 for this system is greater than complexation or sequestering agents, but over time the cost diminishes dramatically because the homeowner is only replacing the filter cartridges at a nominal cost of $15. What this system buys is amazing water clarity at a relatively low cost.
So if staining is your issue, hopefully this information will prove helpful to you. Pricing is likely to change over time, but it seems unlikely that the costs any of the processes mentioned will change dramatically.