Help. Are these black spots black algae or metal stains?

[nmldoc]

I don't know where to start. I have black spots that I need help identifying. I live in Hollister, CA. My pool is 24,000 gallons. We had black algae 10 years ago and I got rid of the visible algae with help from Leslie’s. Unfortunately the method they told me to use raised the copper and CYA levels in the water. The CYA is still high. I know the roots persist. I think the previous owner had black algae originally because he left some black algaecide here when they sold us the house in 2009. I had water circulation problems for awhile starting about a year ago when I had to replace the pump and the filter. I now have those figured out. We started using well water 2 1/2 years ago. When our well was drilled the manganese level was quite high at .452 mg/L. Every time I topped off the pool afterwards, the water would be clear green for a few days. I have read that the combination of iron and manganese can do that. We also have a lot of iron in the water. We had a lot of rain this last year, which may have increased it. The black spots started showing up the end of May when I started topping off the pool every day and there are more all the time. I now have a filter that pretty much eliminates the metals in the well water before it goes into the pool so the water no longer turns green. I have used Jack’s Stain ID Kit on a step of the pool and got clear results. All 4 tests yielded positive results except number 2. On number 1 and number 4 spots, the area actually initially turned dark gray, then cleared eventually. Chlorine (I use power powder plus - I know, I know) and black algaecide containing copper have not removed the black spots. I have turquoise staining which I am sure is due to copper and I also have a few iron stains. A wire brush does not touch the black spots, nor does rubbing a chlorine tablet on them. I have gone from thinking they are black algae to thinking they are metal stains and have gone back and forth treating each, probably making both worse in the process. I have used the cu lator stain removal kit and it does great on the turquoise stains, nothing on the black stains. I have tons of photos I could post. I took these close up ones today of spots on the wall of the pool. They are all taken of the same spot, though not the exact same angle. The first one shows the black spots, the second one shows how they turned brown or green after I used pumice on them and the third one shows them after I then also scrubbed them a chlorine puck. Thank you for any suggestions. I think they are probably black algae at this point, but I know I also have some metal stains and I don't know what to do next.

 

[Texas Splash]

I suspect you have a couple problems:
1 - Almost guaranteed that your iron level is increasing from the well. That will always be a problem unless you use a sequestrant to bind the iron in suspension or better yet, find another source of water. You may also have copper staining which is a completely different nightmare.
2 - This pool has been treated improperly (for years) with pool store testing and products that are ineffective and actually causing more problems. Hence persistent algae and the potential copper problem.

At this point, I suspect a water exchange will be an initial part of the solution, but before doing that let's start with two things:
1 - Rub a Vitamin C tablet on any of the stained areas. Vitamin C tabs will immediately lighten or remove an iron stain. Do that test.
2 - Provide us with a full set of water test results form either a TF-Series test kit (link in my signature) or Taylor K-2006C. If it's not one of those kits, you must get one. It's that important.

Be sure to bookmark and visit our Pool Care Basics for lots of important articles. We'll be here to help.

 

[nmldoc]

Thanks for your feedback. Unfortunately I can’t find a new water source. My original one dried up due to persistent drought in California, which is why we drilled a well. My pool problems really showed up when I started topping off with well water. I do feel that the pre filter I am using the last few months is severely cutting down the amount of metal reaching the pool and I am using a sequestering agent. I have used a vitamin c tablet in the past with no results, but I will try again and I will order one of the kits. A water exchange is possible now that I have the well and pre filter. I would need guidance on how to do it since it is an inground pool and I already have a crack in the pool deck most of the way around the pool. Thanks again for your feedback. I will get back to you.

 

[JamesW]

The pool is probably due for a replaster.

You should get a high capacity filter to remove all metals when refilling.

The plaster looks like is has copper and other metal stains.

The plaster looks like it is worn down to the gunite in several spots.

You might be able to do a treatment with Jack's #2 copper and scale followed by a drain and refill.

 

[nmldoc]

Here are photos taken today before and after I scrubbed the area including and around the middle 2 tiles with a vitamin c tablet. The lower photo was taken before the vitamin c. I would also note that these stains are much more prominent on the wall that is never exposed to direct sunlight. My main question is whether these are "just" metal stains or are they also black algae. James W., thank you for the advise. It probably is due for a replaster. It is hard to get anyone into this area to do it, but I will check into it.

 

[nmldoc]

I did find a pool construction company to come down and take a look.

 

[nmldoc]

The pool is probably due for a replaster.

You should get a high capacity filter to remove all metals when refilling.

The plaster looks like is has copper and other metal stains.

The plaster looks like it is worn down to the gunite in several spots.

You might be able to do a treatment with Jack's #2 copper and scale followed by a drain and refill.

I had a pool construction and renovation company guy come out today. He took one look at it and said many of the stains are probably rebar stains. It makes sense. They responded to nothing. He is going to give me a quote for a replaster and also a repair of a crack in the cement pool deck that will prevent it from affecting the pool itself. The crack is at the outer edge of the pool wall and runs almost all the way around the pool. I know he is a salesman, but this pool is probably over 30 years old and the ground here in California moves a lot. We can start afterwards with clean city water hauled in that is better balanced than our well water. It is probably time to bite the financial bullet and start over with a healthier pool wall and floor before the integrity of the pool itself is affected. I'm fighting a useless battle until I do that. I plan on using this site for ideas to keep the water more safely balanced. Thanks for your help.