Metals in Pool Water
There are many types of metal ions that can be found in pool water. By far, the most common metals found in water are ferric iron (Fe2+) and copper (both Cu+ and Cu2+). Manganese is sometimes found in pools filled from well water.
Metals are a problem in pool water because the ions are not stable or only mildly stable in water solutions at normal pool pH (7.0-8.0).
Chlorine is a powerful oxidizer and it will react with metal ions forming oxidized metal that will drop out of solution and color the water or cause staining.
Water Chemistry Conditions Causing Metal Scale or Staining
The conditions that are most unfavorable for metal ions are both high pH and high Free Chlorine concentrations. Once these conditions occur, the metal ions will no longer stay in solution with water but will oxidize and fall out of solution forming metal scale and stains in your pool. Metal staining is difficult and expensive to correct and remove especially in the case of copper if the stains get old.
Metal Levels in Pools
The easiest rule of thumb for metal concentrations is you want them to be as close to 0 as possible. Typically speaking, iron in concentrations greater than 0.3ppm will start to scale out of solution and form brown water (tea colored) or yellow stains on pool surfaces.
As well, copper ion concentrations above 3ppm will start to scale out of solution and form green colored water and black/brown stains on pool surfaces.
Pool Surfaces Susceptible to Metal Staining
Plaster pool surfaces are much more susceptible to staining because of the higher pH near the plaster surface while fiberglass steps in vinyl pools often show early signs of staining.
Avoiding Metal from Well Water
Commonly well water may contain noticeable levels of Iron that over time will add up and cause staining on the surface of the pool. While there are some ways to remove some of the iron, the easiest way to deal with Iron is to avoid introducing it whenever possible.
One of the best ways to reduce the amount of Iron added is to simply reduce the amount of water you need to add to your pool. Take little steps to reduce your water additions by doing stuff like using a solar cover when possible, tear apart your filter at each cleaning rather than back-washing, and yell at the kids whenever they're splashing too much. Also users have had success redirecting the downspouts from their roofs to send any rain water into their pools to help keep their pool filled.
Metals Added by Alternative Sanitizer Systems
One point to note is that, in recent years, pool builders and equipment manufacturers have been pushing “low chlorine / alternative sanitizer” systems fairly heavily in lieu of traditional chlorine tablet feeders and salt water chlorine generators. These systems still require low levels of chlorine in order to achieve the EPA set standards for sanitation but also pair metal ion systems (Cu or Cu+Ag) with UV Systems and Ozone injectors.
These systems intentionally inject metal ions into pool water as copper metal is an effective algaecide. However, the threshold levels of copper needed are so close to the scaling concentrations that these systems put pool water and surfaces at constant risk of staining.
It is TFP’s recommendation that these metal ion systems be avoided at all costs as they are most definitely NOT trouble-free.
Beware of Metals Added to Algaecides or Trichlor
Metals can also be inadvertently added to the pool water by pool owners. Metal ions were often found in many different commercially available algaecides but, more recently, have been added to many types of “multipurpose” chlorine tablets.
These tablets often contain only partial amounts of TriChlor (a chlorine source) but often have sizable fractions of baking soda, metal salts (like copper citrate or copper sulfate) and weak clarifiers in them. Pool owners are fooled in paying more for less active sanitizer, chlorine.
The key word to look for and avoid is anything that has the work "Blue" in it. That is market speak for copper. These products are something you want to avoid.