Wednesday, August 24, 2011

Question About Greensand Filter Backwash

Thomas Wrote:
Looking at Greensand Iron Filter 7000 1.5 CF (FE008120), I just had a few questions regarding the backwash. Someone told me that greensand filters only backwash very periodically (once every few months) and only needs to backwash frequently if you're using a softener. Your site mentions that it

backwashes every few days. What this person told me doesn't make much sense, but since I don't know much about water filtration, I figured I'd ask the expert.

I also see there is an option for a flow meter for usage based backwash. Is the idea that using the flow meter it will only backwash when it needs to which may be less frequently than every few days (thereby saving pot perm and water in the long run)?

When backwashing, it is mentioned that it usually does this in the middle of the night. Is that because while it is backwashing, the water is inoperable, has poor flow, is noisy, or something else?

And finally, if it is true that it is done in the middle of the night to avoid some kind of conflict or unwanted scenario, what happens when you use the flow meter? Is there a chance it will backwash in the daytime or some other time when you don't want it to?

Thanks in advance. Once I know how often it backwashes and whether I need/want the flow meter, I will be purchasing one.

My Email To Thomas

Hello Mr Tustin -

These are good questions. The greensand media has a fixed amount of iron and manganese it can remove before it gets exhausted and needs to be regenerated. It depends on the amount of iron and manganese you have and if there is hydrogen sulfide (“rotten-egg odor”) present.

See this spec sheet here, from the manufacturer of Greensand-Plus. Assume you had 3.0 mg/L of iron, 0.3 mg/L of manganese and 0.2 mg/L of hydrogen sulfide gas… and were using a 1.0 cubic foot size greensand filter. According to the specs, you could go 2175 gallons per cubic foot of media. If you had a family of four using 200 gallons of water a day, you could go up to around 10 days before it needed to be regenerated.

However, if you had 1.0 mg/L of H2S, the scenario would change dramatically.

It shortens the life of the greensand media to always run it to exhaustion before regenerating it, so in practice most customers find it works best to regenerate it once or twice a week, but the actual number of gallons that can be processed varies widely based on the amount of iron, manganese and H2S present.

Lastly another factor is iron bacteria. Many well waters contain low levels of iron bacteria. The potassium permanganate (or chlorine) rinse will kill this bacteria. However if the iron filter only backwashes once a month or once every few weeks, the iron bacteria will breed inside the filter and coat the media and shorten the life. So generally its best to regenerate more frequently if possible, or better yet use a chlorine feed (chlorinator) ahead of the iron filter to kill the iron bacteria and keep the greensand regenerated.  If you use a chlorinator, no permanganate is used.

Flow Sensor Option

This is a good option as then you can backwash based on gallons and/OR days between backwash.

Timed Backwash

The systems all have timed backwash and typically it is set to backwash during the night when no one is using the water. During the backwash, if someone uses water, the iron filter will allow untreated water to enter the house, it won’t cut off the water supply.

 However, you can just as easily set it to backwash during the day as well. The flow meter option allows the filter to count down to zero from the gallons set, but then it waits until the appointed time day or night to backwash.   

Gerry Bulfin
Certified Water Specialist CWS-IV
Clean Water Systems


We recommend a different greensand filter now, the 7000 has been discontinued.  Please see this link: