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View Full Version : How does polyfilter media work?


LouH
03/02/2012, 08:11 AM
If the stuff pulls out ionic compounds, like copper, out of solution, then why wouldn't it also pull out sodium, magnesium, calcium, other cations, etc?

A question along the same line would be Chemi-Pure resins. I've seen plenty of people use this stuff in their sumps, and their tanks looked great, but again, what is it doing to the water to add value?

Lou

Randy Holmes-Farley
03/02/2012, 09:06 AM
For starters, they do not reveal exactly what the polyfilter polymer is, so I cannot say exactly what the chemical structures are when metals bind.

But, it is not simply an ion exchange polymer and I would not assume that the bonding is even primarily ionic. Metal binding polymers can attach to metals in ways that other cations do not. One can design binding sites for metals that are really very strong and bind little or no simple cations such as sodium when in the presence of an appropriate metal. Ion exchange resins are largely useless in seawater for the reasons that you mention: sodium, chloride, magnesium, and sulfate largely take up all the sites.

For example, here's a drawing from an article of mine on metals in reef aquaria showing how an arrangement of function groups can bind to copper:

Figure 1. A schematic of a copper ion (Cu++; shown in red) being chelated by a naturally occurring humic acid (shown in green).
http://reefkeeping.com/issues/2003-04/rhf/feature/images/image002.gif

LouH
03/03/2012, 08:23 AM
Randy,

Are you an advocate of running a polyfilter full time to adsorb any Cu that happens to enter your system? Are there any risks to doing so?

Lou

Randy Holmes-Farley
03/03/2012, 09:32 AM
I'm an advocate to pulling out copper, but the polyfilter folks put some copper onto polyfilters to keep them from dropping copper below about 40 ppb, which is much higher than my aquarium. So I do not think they will do anything useful in my system, and they might possibly add copper (but I do not know if that happens or not). They certainly can be very useful in copper overdose situations, but diagnostically by color and as a treatment. :)

FWIW, GFO seems to pull out copper, and I do not know if there is any copper preloaded on Cuprisorb but I'd guess not.

LouH
03/03/2012, 09:50 AM
Thanks for sharing your knowledge on the subject Randy.

Along this subject, I have access to an ICP analytical machine. I've been contemplating doing some system monitoring as well as doing some tests to determine Cu content of various sources. I will share these results as I get them. Unfortunately, the ICP does not run full time, so I'll have to wait until is being used to analyze my samples.

Randy Holmes-Farley
03/03/2012, 11:26 AM
Do you know what type of ICP? The ICP-AES that I used could just barely detect the copper I had (~13 ppb) since it was at the limit of detection. An ICP-MS can detect lower, but you may need to sort through various interferences with it. :)

LouH
03/03/2012, 11:50 AM
Icp-aes.