Quote Originally Posted by fedman View Post
Any thoughts...Is the Metal Free product a waste of time?
Yes, it's probably a waste of time, assuming that THIS:



is what you're talking about. I'm not sure what's in it; the 2005 MSDS indicates that at that time, it was EDTA. A newer 2010 MSDS indicates that it's a low concentration of citric acid. Here are snips from those MSDS sheets:

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The problem is, neither EDTA nor citric acid are really chlorine compatible. I think they might work OK in a Baquacil pool -- EDTA is what's used in THEIR metal product, but basically you destroy the Metal Free when you chlorinate.

The sequence you have to follow to REMOVE iron stains like yours is
1. Lower chlorine
2. Add ascorbic acid (vitamin C) to dissolve stains + Polyquat to prevent algae while chlorine is low + HEDP to KEEP the dissolved iron, dissolved.
3. Re-chlorinate, destroying the ascorbic acid, which is then picked up by the HEDP, before it can restain.
4. Filter 24/7 with a CuLator in the skimmer, allow the CuLator to remove the iron from the water that contacts it. Some iron is also likely to be released, but end up in particles on the filter.

None of these steps work on their own. Using Vitamin C (or citric acid, through it's less effective) dissolves the iron, but then releases it to re-stain as soon as the pool is again chlorinated.

EDTA acts like HEDP, and can't really DISSOLVE iron that's already a stain, but it can keep iron in solution. However it's weaker than HEDP, and is MUCH more rapidly broken down by chlorine. So, using EDTA may *keep* iron from new water dissolved, but it can't dissolve iron that's already a stain, and neither EDTA nor HEDP do ANYTHING to actually remove the iron from the pool.

Likewise, the CuLator can't work alone. Iron in pool water tends to be rapidly oxidized by chlorine to a stain or particles -- so that when you add chlorine to water with iron in it, you QUICKLY* end up with water that has ZERO iron *in* the water. You may have terrible stains, but hardly any iron dissolved IN the water. Since the Culator ONLY works with dissolved iron, it's useless, unless you FIRST re-dissolve the iron, and then use HEDP to KEEP it dissolved in spite of the chlorine.

* an exception: bacterial nodular corrosion seems to involve enterobactin, an extremely strong chelant, much stronger than HEDP and possibly also quite chlorine resistant. In this case, you may have highly chlorinated water that ALSO has a lot of dissolved iron.

. . . I hope this is clear.