Copper Stains

[Steve456]

When we closed on our house we discovered that the previous owners stopped pool maintenance when they accepted our purchase offer. We inherited a pool with mustard algae; however as pool newbies we did not know that. We brushed the pool until our arms fell off. My wife was convinced that our sand filter was leaking sand into the pool. A pool store recommended using copper algaecide. Finally, we had clear water. For the past 4 years we have used some additional copper algaecide since our pool seems to be prone to mustard algae - not green algae.

We have now developed black or gray staining in the deep end around the drain. We throw calcium hypochlorite in the deep end and since the hypo takes time to dissolve I think some of the hypo sits on the bottom of the pool. I assume that stains are copper stains. We are planning on installing a SWG and I want to get rid of the stain and properly balance the pool before the install. [I read the sticky on ascorbic acid treatment.] Our current water chemistry is:

Free Chlorine: 3.0
Combined Chlorine: 0.0
pH: 7.6
Total Alkalinity: 70
Cyanuric Acid: 60
Copper .7
Water Condition: Crystal clear
Tests Using TF100 Test Kit and Taylor copper test kit

I found it difficult to test the black area in our 10 foot deep end. With the pool pump off I tried a Rube Goldberg arrangement to hold vitamin C on the bottom of the pool. The vitamin C did not lightened the stain. The vitamin C was on the bottom of the pool for approximately 15 minutes.

I have several questions for the chemical/water pros that contribute to help us struggling pool owners:

Is there a treatment other than ascorbic acid for copper stains?
Some of the stains in the shallow end have gotten lighter. Will continued chlorine use or the sun lighten the stains?
What is a good method for testing a stain in the deep end of the pool?
How long is copper algaecide effective? Can we stop using copper algaecide and the problem will improve without treatment?
Will adding a sequestering agent now help to remove the stain?
After we resolve the staining we will add borax to the pool. Since borax raises the pH & a high pH can precipitate the copper what extra precautions should we take to avoid restaining the pool? Or should we add borax first?

TIA in advance to Waterbear, JasonLion, chem geek, duraleigh, SeanB and the many other knowledgeable contributors.

 

[ktdave]

Refer to THIS thread.

As waterbear stated, be careful....

Be careful using ascorbic acid on copper stains. It can sometimes make them worse. Try holding a vitamin c tablet on the stain. If it disappears then ascorbic acid can work. If it turns black or brown don't use it.

 

[Steve456]

A thank you to ktdave for the quick reply.

An update to my vitamin C test. Two hours after I removed the vitamin C tablets from the pool bottom the grey/black stain has turned a yellow/tan color. I noticed this in the shallow end test earlier and the yellow stain improved over night. Maybe ascorbic acid will work.

TIA

 

[JasonLion]

Black copper stains can be very difficult to remove sometimes.

Copper remains in the water and is only lost through splash out and water replacement. You can measure the copper levels to see if you have an effective level of copper. Higher copper levels are very prone to staining, so have a care about adding too much copper based algaecide.

One test to try is to put some dry acid in a sock and hold that against a spot of stain for 30 seconds and see if anything changes. The sock can be tied to the end of a pole.

One suggestion is to use a diphosphonic acid based stain remover applied directly to the stained areas.

Be very careful about anything that raises the PH, as this can lead to more staining. You can lower the PH to 7.2 to give yourself more safety margin, but adding borax will very likely lead to extensive staining.

 

[Steve456]

Jason thank you for the ideas.
My copper level is approximately .7.
Is a diphosphonic acid based stain remover the same as a HEDP sequestering agent such as Jack's Magic Blue Stuff? Does a copper algaecide lose its effectiveness over time? Can we stop using copper algaecide and the problem will improve without treatment? Some of the stains in the shallow end have gotten lighter. Will continued chlorine use or the sun lighten the stains? Will adding a sequestering agent now help to remove the stain?

 

[Guest]

A thank you to ktdave for the quick reply.

An update to my vitamin C test. Two hours after I removed the vitamin C tablets from the pool bottom the grey/black stain has turned a yellow/tan color. I noticed this in the shallow end test earlier and the yellow stain improved over night. Maybe ascorbic acid will work.

TIA

If vitamen c will work it will do so in about 30 seconds when you test with a tablet. If the black stains turned brown or tan you are likely converting it to a form of copper stain that is very difficult to remove.