I put this in the deep end rather than the review section since I thought it more appropriate here. Might get some more chemistry discussion that might not be of general interest.

As I posted on another thread, I recently bought a Metal Trap. These are advertised to remove iron and copper (mainly iron, I believe) from water before adding it to the pool. How it actually works is not included in the literature, but my best guess is that it uses pretty standard technology. The basis behind it is a type of substance called green sand. It is basically a sand material that is coated with manganese oxide. The iron containing water passes though the sand sieve and reacts with the iron dissolved in the water. The oxidized iron is then filtered. What comes out is supposed to be iron free, or pretty close. Like I said, the technology has been around a long time but mainly used in water treatment plants.

So on to my story. For most of the year, my town water is really iron free, less than 0.2 ppm. However, in the summer months starting in mid June through mid September, the iron content goes up to around 1-2 ppm. This is because the town uses a supplemental well to make up for increase summer water usage. It’s dissolved iron (reduced) so you don’t even see it in the water. But…does it sure stain the bathroom fixtures and the pool. Every year when I add top off water, I have to add sequesterant . Once the water hits the pool, over time the chlorine oxidizes a bit out and turns the water a nice light green until I add a few ounces of Jack’s or HTH. The HTH fixes it right up, but I really don’t want to add iron at all, so I bought the Metal Trap.

I got a 25,000 gallon capacity filter, this is it’s supposed to filter up to 25,000 gallons of water as long as the metal is at or lower than 3 ppm, or so. Anything more, and the gallons filtered goes down. The filter comes with a ball valve that fits on the end where the water enters. The directions say to cut the flow down into the filter if you don’t get good results. The slower the flow, the more iron it converts and filters, or so they say.

I did some tests and will post the results below. I tested the straight tap water and then tested the flow out of the filter at 3 different flow rates, full on, half, and quarter on. Full on gives me around 6 gallons per minute, half gave me ~4 gallons, and quarter about 2 gallons per minute. I tested the iron content using the Taylor iron kit. It’s a color test that uses a comparator that actually has liquid iron standards in the comparator block. It’s a bit hard to see and differentiate, but my eyes may be to blame as well. I did the test 2 times to see the variability. I rinsed the tube with deionized, distilled water in case anyone is wondering. So here is what I got.

Tap water: >1, but less than 1.5. (I called the water company and they said right now its running at around 1.3 ppm, so the Taylor kit was pretty close.

Full open filter: 0.6, 0.8

Half open filter: 0.6, 0.6

Quarter open: 0.4, 0.4

From what I’ve read, 0.3-0.4 ppm is where iron starts to become an issue in terms of staining. I mentioned yesterday on another thread I was less than impressed, but at that point, I had only tested the tap water and full flow. Not sure what to think now, but I guess 0.4 from 1.3 is ok, maybe expecting lower was too high of an expectation. I’d be interested to see how low it would go if you had iron in the range of where some wells are (>5 ppm). I havent added any water to the pool yet; when i do I'll up date as to what happened.

Admittedly not perfect, but 0.4 is still way way better than 1.3 from the point of view of the swimming pool.

Green sand filters work better when you use a relatively large filter at a relatively slow flow rate. The higher the amount of dissolved iron, the more important both of those factors become. To filter out 5 ppm you would want a much larger filter than the one you were using, or need to run it at a much lower flow rate (or both).

I agree there. It seems that the change in iron above 0.3-0.4 it becomes a staining problem, so getting it to those levels will be good.



Metal Trap sells a 50,000 gallon filter, so i imagine its bigger. The 25,000 gallon i got is about 2.5 feet long and about 3.5 inches in diameter.
Not sure you can run the flow rate much lower, though. I was able to get the ball valve lower than a quarter on, but the flow rate was just a trickle. I didnt measure the gallons per minute, but my guess was maybe 1 or less.

The ball valve that came with the filter is not that great. It's pretty hard to control and vary the flow rate that well. I may get a better valve and see if i can regulate it better. That being said, I'm not sure a lower flow rate would get the ppm's down much lower. I would like to know from others on TFP that have iron in their fill water what the levels are, just for comparison.

That kinda sucks, but thanks for posting. At quarter flow it would take a while to add a couple inches, but you sure couldn't fill a pool at that rate.

BTW, I thought you had a whole house iron filter. What happened to that?

I was going to get one and just tie it into the outdoor hose bib. But, it was almost $300 and it still was not one you could backwash and re-use. You still had to buy replacement cartridges.
This was half the price and now im not convined the other one i was looking at is much better than the one i got.

For folks that Google/Bing up this 2009 thread, as I did...............

I've seen the suggestion to use a submersible pump and just keep recirculating the pool water through the Metal Trap. Based on the information in this thread I'm going to try this. I have a Sears submersible pump with a regular garden hose threaded outlet and several 10-foot sections of garden hose that I bought at Home Depot/Lowes.