Testing for Iron with Sequestrants in the water

[TreeFiter]

I've been trying to get some good test results on a pool that I know has iron in it. I know this because I just did stain removal on some really bad iron stains that covered the entire pool. I've tested several times at different stages of stain removal, most recently when 99% of the staining was gone. In all of the tests, I came up with 0.1ppm.

I've read that sequestrants may interfere with test results for iron. I believe I also read somewhere that if you wait longer, the test will eventually account for the sequestered iron. I let a sample sit for about 8 hours today, and it still only said 0.1ppm. Is there any way to get an accurate reading on the iron in this pool?

I've been using a LaMotte test kit. It has a tablet, and then I add 5 drops to get a color change if iron is present.

 

[chem geek]

Sorry no one responded sooner. Whether metal will show up in a metal test kit depends on how strongly the metal binds to the metal sequestrant compared to the indicator dye or other chemicals used in the metal test. If the metal sequestrant binds very strongly, then it may not show up in a metal test. I don't know how to resolve this except to use a test that uses some sort of chemical designed to very strongly bind to the metal and remove it from a sequestrant and then be able to be tested itself. Your question is probably one for LaMotte technical support.

 

[TreeFiter]

Thank you chem geek. I tried to contact LaMotte, but they haven't responded to my emails.

I had a conversation with an environmental lab, and they said their test would be able to detect all of the iron present as a result of the digestion process they use. I believe they use concentrated Nitric Acid.