Can Tree Leaves Cause Metal Stains?? (Yes....a very weird question)

This might be a real head-scratcher. I know it has been (and still is) for both me and the local pool supply/maintenance company.

Here’s a recap of our current situation:

• 14,000 gallon in-ground concrete pool in Durham, NC
• Completely refurbished in Spring 2011, including new epoxy coating and new Aqua Comfort heat pump
• There is a check valve between the chlorinator and the Nature2 cartridge holder; the new heat pump is upstream from the Nature2
• When pool was filled, water was run through a Metal Trap filter
• Top-offs during the Summer were not run through a Metal Trap
• Municipal (Durham, NC) tap water is high in phosphates, but pool was treated with Natural Chemistry PhosFree after filling and Pool Perfect+PhosFree during the Summer. Phosphates were kept at a very low level.
• No significant water quality problems during the Summer
• Trees around the pool are mostly several varieties of oaks. There is a mimosa and one small pine tree.
• Pool heat pump was turned off in late October, so water temperature dropped into the 40’s-50’s
• Pool is not closed or covered during the off-season
• Most leaf fall occurred in November and early December
• During leaf fall I raised the chlorine to 5-10 ppm because of all the organics in the pool
• Pool became stained. There was a general stain over most horizontal surfaces, and darker stains where leaves had rested on the bottom. There was some staining on the walls.
• Chlorine shocked the pool, which should have removed tannins, but there was no effect
• Scrubbing the stains had no effect
• Pool company water testing showed no copper or iron in the pool water.
• Lab director at municipal water plant says that manganese levels in tap water are below detectable levels
• Putting citric acid directly on the stains using a sock did not immediately remove the stains, but there were some broad swaths of lightening of the stain from where the sock had been applied.
• Dropping Vitamin C (ascorbic acid) tablets on the stains *immediately* removed the stain around the tablet. This is the most definite indication that the stains were some form of metal.
• Over the next few days most of the stains gradually disappeared. pH and chlorine levels also dropped.
• Putting pieces of chlorine sticks directly on the remaining stains (where leaves had sat) did not remove the stains.
• After a few more days all the stains finally disappeared.
• My fiancée recently remembered that the previous owner of our home recommended keeping chlorine levels low during leaf fall. Our (faint) recollection is that he mentioned problems with discoloration of the water and not staining of the pool walls.
• Spoke with Natural Chemistry. Based on the evidence that the stains were metal-related, and based upon water tests at the pool supply company that showed no copper or iron, they recommended using ScaleFree instead of MetalFree to chelate whatever metal might be in the water. They also said that a filter aid is not necessary since we have Zeosand in our sand filter.

It appears that the tree leaves are somehow depositing a metal into the pool that causes both general staining and darker stains where the leaves set for a few days. (I’m even wondering if we are living on top of some sort of toxic waste dump and the leaves are picking up a metal from groundwater.)

In hindsight we were probably dealing with the same problem in the summer of 2010 (our first year owning the house and pool). There was copper in the water and staining from a rotten gas heater core, but after we got the copper out we went through several more cycles of ascorbic acid/MetalFree to remove stains, but the stains would reappear as soon as the chlorine levels were raised. We finally broke the cycle by using ScaleFree instead of MetalFree. There probably was metal in the water from the previous fall.

Has anybody ever heard of tree leaves causing metal (and not tannin) staining? If so, do you know what metal the leaves might be depositing in the pool?

Does anybody have any recommendation for next fall? My current plan is to keep chlorine levels low, use high maintenance levels of ScaleFree and treat the staining, if there is any, with citric acid followed by ScaleFree.

Thanks for any information and suggestions that is posted.

What you are describing sounds like reversible iron staining. It's something I've experienced several times, and yes, there has to be an iron source, but I'm pretty sure it's not your leaves.

My guess is, the iron was ALREADY there, but adding the chlorine (to prevent leaf stains) oxidized the iron and cause the stains. Adding all the chelants, and letting the pH and chlorine drop allowed the iron to reduced and returned to a soluble form.

When I've experienced it, the most common source of iron has been municipal water supply pipes, but some salt (for SWCGs) is reportedly iron contaminated, and I've seen iron contaminated stabilizer myself.

If you are running within Nature2 guidelines -- a useless gadget -- then you are keeping pH and chlorine low enough so that iron will not be oxidized out (ideally on the filter) and then removed. As a result, even small amounts of iron will build up in your pool water.

Here's an easy check: if the INTERIOR of your toilet tanks is orange-brown, you have iron in your house water. If you fill your pool with the same water . . . you are putting iron in the pool water, too.