Removing iron stains from my plaster pool

[midnightpainter]

I bought a house with a pool about a year ago. This week, after using shock, ugly stains formed all over the surface.
Turns out that, among the dive toys in the deep end, there was a piece of metal that had been down there long enough to rust. I used a cut lemon on one stained area, and it turned bright white. I'm pretty sure it's iron stain.
I've ordered the HTH 6-way test kit, and carefully read a lot of information on this subject. I'm kind of a newbie at this, so I wondered if I might ask ...
When I'm ready to raise the chlorine again (after using the poly 60 and ascorbic acid and ProTeam Metal Magic) what does "minimum chlorine for your cya according to the "best guess chart"" mean? Should I just pour in bleach, and if so, about how much? Also, what is the best way to (carefully) raise the Ph and alkaline?
I checked, and I don't believe the fill water contains iron. How long should I use the Metal Magic? Will the DE trap the sequestered metal, or do I have to use CuLator? How quickly, and how often, should I backwash?
I'd really like to get this right -- any help would be greatly appreciated!

[PoolDoc]

Sorry it's taken so long to respond; I've been under the weather, recovering from a bout with Lyme disease, and several moderators have had other issues.

You've obviously been doing quite a bit of reading, but so let me see if I can clarify the process a bit:

1. Re-dissolve the metal causing the stain. With iron, ascorbic acid (vitamin C) works. Citric acid (lemon) and ascorbic acid both are destroyed by chlorine, but the byproducts from citric acid + chlorine are not quite safe for people.

2. Keep the dissolved metal in the water, so you can remove it directly (slowly => CuLator) AND so you can filter it (hopefully) as it comes back out of suspension. If you don't add something to KEEP the metal in the water, it will tend to re-stain as soon as you add chlorine and destroy the ascorbic acid. The best product for keeping the metal in the water is HEDP -- a phosphonic acid derivative, that adds phosphates to your pool water once it breaks down. HEDP is the *most* chlorine stable of the metal chelants (keep metal dissolved or suspended).

3. Filter constantly, so (hopefully) as the metal UN-dissolves, it ends up on the filter, rather than back on the pool.

There are some points you need to consider:

+ The Culator packets seem to work, but they can only remove metals from water that comes into direct contact with the beads in the packets. If you simply buy the standard packet, you probably will not remove enough iron during the life of a dose of HEDP, to completely prevent re-staining. Buying multiple packets and lining your skimmer basket will increase effectiveness. Using a skim-sock will help prevent contamination of the CuLator packets. If you can prevent them from being contaminated, they seem to last much longer than the company claims.

The *best* place to put the Culator units would be DOWNSTREAM of the filter, but the only way to do so, is to jury rig something to hang the packets in front of your returns, or put them in the return piping. If you try this, be careful NOT to obstruct your pool's flow.

+ Calcium dust seems to pick up metals pretty readily. If you want to pursue it, using calcium hypochlorite to chlorinate, by adding it DIRECTLY to the skimmer, that will tend to both UN-dissolve the metals (high chlorine) and trap them on the filter (calcium and calcium carbonate from the cal hypo). BUT . .. there are numerous cautions that apply to this method. You MUST make CERTAIN that cal hypo does not contact any other chemicals -- including stabilizer, trichlor taps, etc.!

If you want to pursue this, you'll need to post test results on your pool's pH, alkalinity, and calcium levels, and a description of any chlorine feed system you have.


+ The fullest exposition we have to date on stain removal is here:
http://www.poolforum.com/pf2/showthr...acid-treatment

Links to Amazon for many of the products are present.

But we're finding that many users have to repeat the process at least 2x to get to remove the stains AND keep them off. Most users also have to go to some sort of maintenance process, to prevent re-occurrence. That may not be necessary for you, if the metal source was transient (a piece of rusting iron, now removed)

+ HEAVY localized iron stains are best removed with sodium hydrosulfite. Iron Out is your closest approach to this -- it contains both 'hydro' and sodium sulfite.