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About Greensand Filters

Q. What are “greensand” iron filters?

A. Green sand filters use a specially formulated filter media made from a naturally mined form of glauconite greensand. The greensand filter media has a special coating of manganese oxide, which oxidizes iron, manganese and iron in the water upon contact with the filter media.

Greensand filters require a type of purple powder, potassium permanganate to regenerate and clean the greensand filter media.  An alternative to Greensand Iron Filters are the Pro-OX non-chemical air charger iron filters.


Q. How does a Greensand Filter remove iron and manganese from water?

A. Iron and manganese are metals often found dissolved in water. Iron and manganese cause stains when exposed to air in the laundry, bath, etc. by oxidizing or “rusting.” The greensand filter media oxidizes dissolved iron and manganese on contact as the water flows through the greensand filter which causes these elements to precipitate (or form solids) in the bed of the filter.

The iron filter backwashes these small particles to drain every few days in the middle of the night (or some other preset time), thereby cleaning and restoring the filter media. To provide the oxidizing power to precipitate these metals, the filter is automatically cleaned and restored with potassium permanganate (a purple liquid) during each backwash cycle.


Q. Is potassium permanganate toxic or harmful?

A. Potassium permanganate is a powerful oxidizer and, similar to chlorine, can cause skin irritation or burns if direct contact were to occur. But, no permanganate is added to the filtered water. The permanganate is only used to backwash and clean the greensand filter media. A special rinse cycle makes sure the filter bed is free of any permanganate residual.


Q. What is the difference between “greensand filters” and “greensand-plus filters”?

A. The difference between a Green sand filter and greensand-plus and manganese greensand is in the substrate that forms the core of the media and the method by which the manganese dioxide coating is attached to that substrate.

GreensandPlus has a silica sand core and the coating is fused to it while Manganese Greensand has a glauconite core and the coating is ionically bound to it. The silica sand core of GreensandPlus allows it to better withstand operating conditions in waters that are low in silica, TDS and hardness.

Greensand-plus does not require potassium permanganate, but it does require one feed in chlorine ahead of the greensand-plus filter. If you are planning on using a chlorination system or a chlorinator we usually recommend greensand-plus iron filters.  If you don’t plan to chlorinate (or use ozone) ahead of the filter system, the regular greensand filter works better.


Q. Do Greensand filters have any special conditions in order to work properly?

A. Yes! There are very specific conditions required. The water must have a pH of 6.7 to 8.8. If the water has a pH of less than 6.8 we usually recommend treating the water first with a neutralizer filter or a soda ash feeder. The best applications have feed or raw water of less than 15 PPM of iron and manganese, combined. The maximum practical removal rate for hydrogen sulfide is 5 PPM. The water should contain no tannins or oil.

Q. My water has a very bad smell of sulfur, will this be removed?

A. While these greensand filters will remove up to 5 PPM of hydrogen sulfide, in some cases the odor can be coming from conditions that exist after the water enters the plumbing. For instance, water heaters often have decaying anode rods that create hydrogen sulfide gas, so that even if the water entering the water heater is clean and odor-free, you can still have an odor problem.

It is important to identify the source of the odor and to verify that it is in the cold water also, which would indicate that all the incoming water has an odor. In many cases, a thorough sanitizing of the household plumbing with chlorine is recommended after installation.  


Q. If I want to use a chlorinator for my water, can I use this type of iron filter?

A. Yes. These iron filters actually work better with a chlorine feed. With chlorine pretreatment, permanganate is not usually required.


Q. I would like to use the Greensand-Plus or Greensand filter, with a chlorine injection system, but I don’t want chlorine in my house. What can I do?

A. You can use a backwashing carbon filter after the Greensand filter to remove all chlorine before it enters the house.


Q. I have very high manganese (greater than .05 PPM), will these iron filters remove manganese also?

A. Yes, these systems work great to remove manganese, both dissolved and oxidized. For manganese removal, the Greensand filters are an excellent option, as many iron filters do a good job of removing iron but do not do a good job at removing manganese.  Pro-OX filters also remove manganese however and do not need or use potassium permanganate.


Q. What maintenance is required for the greensand filters?

A. Once every one to three months depending on how often the iron filter is set to backwash, a few pounds of dry potassium permanganate powder is added to the little solution tank. Once a year there is some general maintenance that should be done to the iron filter and permanganate solution tank, which takes about one hour. No special tools are required.


Q. How frequently do I have to replace the greensand filter media?

A. The filter media will last for 4 to 8 years depending on usage and conditions. It is easily replaced.

  • Clean Water Systems & Stores, Inc., Water Treatment Equipment,Service & Supplies, Santa Cruz, CA

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