Can't Get Rid Of Metal

[johnboy]

I have a 15' above ground pool that I topped off (18" of H2O)with my well. I filtered the water before putting it in but alot of iron got into the pool. Before adding the water it was clear from the winter, but turned green after adding the water. I had the water tested and it was positive for Iron and coppper. I have since added two bottles of metal magic and the pool will clear up and look very nice for a little while then it goes back green again. I think what's happening is the metal is going into solution, but not getting trapped in the filter (using a cartridge filter)???? I'm not sure what to do next?????? Is there that much metal that I might need another quart????

Thanx

[chem geek]

Metal sequestrant will slowly get broken down by chlorine so more needs to be added. Read Metals in the Water and Metal Stains to find some good sequestrants that won't break down as readily. Nevertheless, you will still need to add a maintenance dose of sequestrant even with the better products, but they won't be consuming chlorine quite as quickly and the maintenance doses can be less.

You cannot filter out metal ions. You can only filter out solid metal, but that's not likely to be your problem. If it is, then a clarifier can help if your filter isn't good at filtering finer particles. However, I suspect that you've got metal ions, not solid metal, since the sequestrant will only combined with metal ions to prevent staining and colored water.

[PaulR]

Hi Richard, have you checked out this topic which claims some success with removing iron? I know my dad used to use chlorine to try to precipitate out iron while we were filling the pool where I grew up.

--paulr

[chem geek]

Paul,

There are two very different types of iron (I'm being simple here). There's solid iron particles, or particles of iron oxides, and then there's metal ions themselves. The former can be filtered out so yes, that is very effective. The latter cannot be filtered out so must usually be sequestered (held in solution) by use of a metal sequestrant.

Now one can try and force precipitation of metal ions using a combination of chlorine to oxidize ferrous ion (Fe²⁺) to ferric ion (Fe³⁺) along with high pH which is likely to from ferric oxide or ferric hydroxide (or ferric oxide-hydroxide). Using a hypochlorite source of chlorine will give you both the chlorine needed for oxidation and the higher pH needed to form solids. If this is done off-line, then these solids can be filtered.

A similar approach raises the pH and increases the TA to increase the carbonates level to precipitate ferric carbonate. I believe this is the primary method used in some off-line Calcium Hardness (CH) removers that should also help to remove iron ions as well. So well water that is too high in CH and may have metals (and may be high in TA as well) can have the pH forcibly increased (and some chlorine added to oxidize iron) to lower both calcium and iron levels. After removal of precipitate (including fine filtration), acid is then added to bring the pH to normal levels. The result is saltier water (i.e. sodium chloride) that is lower in CH and metal ion content.

I just wrote up a description on metals and staining in two posts here.

Richard