Stains on pool walls - what are they and how to rid?

[acoutee]

Hello -
I have a stain on the plaster walls of my pool that extend about 2.5 feet underwater from surface and then stops; there is a visible horizontal line around pool at that depth, below which there is no stain (see attached picture). I'm not sure whether this is a metal-type stain or an algae stain. I'm looking for guidance as to the best way to diagnose and treat.

Background: Earlier this summer, I went on vacation for a couple of weeks and had a green algae issue when I returned. I followed instruction on this site to resolve the issue, which I think it is now under control (no re-emergence for ~1 month). I first noticed this 2.5 ft deep wall stain after having resolved the algae issue, but I'm not sure if it is related or I only noticed because I was now paying more attention. Perhaps unfortunately(?), I also used Regal Algaezone Plus (which contains copper) during my battle with the algae. Based on tests I was getting at the pool store during that time copper levels did come up a little but have since gone away (perhaps the copper attached to my wall).

Quick test: As I was adding muratic acid tonight to lower pH, I decided to run a quick test. I poured a little acid close to the wall (more quickly than I usually would) and scrubbed the plaster near surface with a brush. This definitely removed the stain in that location, but it was a locally high concentration of acid. Normal brushing does nothing to remove the stain.

Current Levels:
FC - 3
CC - 0-0.5
pH - 8 (before my acid addition above, but my pool typically runs this high; no matter how much acid I add, within a week it has increased to this level again)
TA - 80-90
CH - 275
CYA - 50

Thanks in advance for your advice.

 

[chem geek]

Welcome to TFP!

You wrote that you followed the instructions on this site, but that you also used Regal Algaezone Plus which contains copper. That is not following the instructions on this site described in the Pool School. Under Recommended Pool Chemicals we do not list any algaecides (nor clarifiers, flocculants, enzymes or other chemicals). Under Defeating Algae it says the following (bold emphasis mine):

Algaecides rarely help and often cause problems. Copper based algaecides can cause unsightly copper stains that are difficult to remove, and can turn blond hair green. Linear quat based algaecides can cause foaming and bad smells. Polyquat based algaecides can be used as a preventive measure, but are ineffective at fighting algae once you have it. Polyquat is particularly useful when you are unable to maintain the FC level, such as over the winter or during an ascorbic acid treatment.

Under Metals in the Water and Metal Stains it says the following:

Iron is fairly common in well water but rare in municipal water. If you will be filling you pool from a well, have the water tested for iron. If you have iron consider having iron free water trucked in. Copper is in some algaecides, many "mineral" systems, and ionizers. If the PH in the pool goes much below 7.0 for very long, copper can get into the water from a copper heat exchange coil, commonly found in pool heaters. In addition to staining the pool, copper can turn blonde hair green.

According to this MSDS, Regal Algaezone Plus contains "citric acid", "copper carbonate", "monoethanolamine", and "triethanolamine". Unfortunately, they do not list the actual percentages of copper. Would you please look at the bottle and let us know exactly what volume of Regal Algaezone Plus you added, how many gallons of water are in your pool, and the EPA registration number listed on the algaecide product? We can then figure out how much copper you actually added to your pool. If the EPA registration number is 8959-2, then as described in the PAN database, this is 51.4% copper ethanolamine complex which according to this EPA document is 7.41% elemental copper or 0.72 pounds of copper per gallon of product.

If you were to hold some ascorbic acid against the stained area, then if it were not to fade very much but does so with acid, then that's not an iron stain but either a copper stain or an organic stain. If you were to hold some chlorine against the wall such as Cal-Hypo or Dichlor or lithium hypochlorite or even chlorinating liquid or bleach if you put some in a bottle you can hold against the wall, then if the stain fades it's organic and if it doesn't then it's likely copper. Trichlor is harder to use to figure this out since it is both acidic and high chlorine so doesn't readily distinguish between an organic stain and a copper stain.

If this is a copper stain, then it is VERY hard to remove because as you found it generally takes acid to remove it and that will end up damaging your plaster surface. This is why we are so against taking the risk of such copper staining by using any copper-based products.

Also, your FC level of 3 ppm is too low for your CYA level of 50 ppm based on the Chlorine / CYA Chart where the absolute minimum FC is 4 ppm for 50 ppm CYA.

The fact that your pH tends to run high, which earlier this year was certainly due to the new plaster, can be lessened by keeping your TA lower at around 70 ppm. Certainly, letting the pH get towards 8.0 isn't helping with the metal staining as metal stains at higher concentrations of metal and at higher pH. If you do decide to maintain a lower TA level and if you are able to maintain a pH not higher than 7.7 or 7.8, then you might consider raising the CH level some to balance the saturation index, but that's something to deal with longer term after treating the metal staining.

 

[acoutee]

Many thanks for the quick and detailed reply. I recognize the error in my ways... the algaecide treatment was initiated before I followed instructions on this site.

The Algaezone Plus used is EPA Reg No 8959-2-4217, with ingredient/concentration you list above (51.4% copper ethanolamine complex, 7.41% metallic copper equivalent, 0.72 pounds of elemental copper per gallon of product). In total, I used 32 fl.oz. of this product. My pool is 22k gallons.

I will try the ascorbic acid and chlorine tests described above and post the results.

 

[chem geek]

So you added 0.72*(32/128) = 0.18 pounds of copper to your pool which is 81,647 milligrams. Your 22,000 gallon pool is 83,279 liters. So the copper concentration in the water is 81,647/83,279 = 0.98 mg/L (ppm) which is certainly high enough to cause staining especially when the pH gets higher. So while the tests will confirm it, it seems very likely that your staining is copper and unfortunately is hard to remove. If the stain is fairly new, you've got a better chance of removing it by lowering the pH of the pool water or if that doesn't work then do a more general acid washing treatment over the affected area.

The use of metal sequestrants that work better for copper removal would also be done, most likely Jack's Stain Solution #2 - The Copper and Scale Stuff. A good part of this stain treatment simply lowers the pH to around 6.0 (the MSDS does not say, but the product appears to contain a sulfur/sulfate/sulfite/sulfide product and their instructions indicate using Muriatic Acid to lower the pH), but since they say the ingredients are proprietary I do not know if simply lowering the pH is sufficient. You bypass the heater when using this product (after all, if it removes copper by lowering the pH and/or other means, then that won't be good for your copper heat exchanger). Note that in addition to this product that removes the stain, you use a metal sequestrant to keep the copper from redepositing -- Jack's Magic® the Blue Stuff® would be used.

Over time, you'll want to physically remove the copper from the pool which usually means replacing the water in your pool to dilute the copper out. You could also consider using CuLator® if water is expensive and replacement unlikely.