@ Jeff - I copied your post to this new thread: Using-HydroPureTech-cartridges-to-deal-with-Iron

@ jrsdws - Sounds like you're making progress, with the Ferritabs, and with your other actions. Metal removal is NOT a process that we've mastered here, so every good result especially when all the details are recorded as you've done, helps us.

The Ferritabs seem to be a polyacrylamide (PAM), originally formulated by (or for) Aqua Clear (Chemtura / Bioguard), now owned and marketed by www.michiganswimmingpoolservices.com / askthepoolguy.com.
This trademark for FERRITABS was filed by BIO-LAB, INC.; Biolab Services, Inc; AQUA CLEAR INDUSTRIES, INC.; HYDROLOGY LABORATORIES, INC.. On 7 October 1974 this trademark was filed, on 6 January 1976 this trademark was registered and on 6 January 2006 this trademark was renewed.
http://goo.gl/JnTnF => www.trademarken.com


polyacrylamide on Wikipedia

I was curious why, if the product works, Aqua Clear would have dropped it. But I found this article:
Acrylamide release resulting from sunlight irradiation of aqueous polyacrylamide/iron mixtures
J Agric Food Chem. 2008 Apr 23;56(8):2773-9. doi: 10.1021/jf703677v. Epub 2008 Mar 20
download here: http://www.researchgate.net/publicat...eiron_mixtures
From the Wiki article, it appears that un-polymerized acrylamide is a toxin of concern with respect to consumer use of PAM. The article listed above apparently reports data suggesting that PAM + iron + sunlight releases acrylamide. My guess is that the evidence is non-conclusive OR that the quantities released are not really problematic. But, big consumer companies (like Chemtura / Aqua Clear) don't want products that have a bad rep, if it's undeserved. So I'm guessing that Chemtura may have looked that the small profits (for them) from the product, and the possibly large PR risk, and decided to dump it.

Of course, that's ONLY a guess. However, it appears that you might be a bit safer using the FerriTabs, if you keep the pH high, near 8.0:
Linear anionic polyacrylamide (PAM) has been used in irrigation practices as a flocculating agent to minimize water losses through seepage in earthen canals. The stability of PAM is of concern because of the possibility of acrylamide (AMD) monomer release during environmental weathering. Aqueous solutions of commercial PAM mixed with ferric sulfate, subjected to simulated and natural sunlight irradiation, showed polymer chain scission and release of the AMD monomer. At acid/neutral pH, the amount of AMD released was directly related to the concentration of ferric ion and the irradiation time. At alkaline pH (∼8), PAM/Fe3+ mixtures were stable under irradiation. (highlight added by PoolDoc) PAM chain scission involved the hydroxyl radical, but specific AMD release appeared to require PAM-bound iron. Low iron concentrations and alkaline pH of irrigation water would limit AMD release. Residual monomer in PAM can contribute AMD to irrigation water, but concentrations would remain below the U.S. EPA drinking water standard of 0.5 ppb.