Can't Get Rid Of Black Algae - Tried Everything

[Gavin]

I have a painted pool and the black algae keep coming through the paint. I tried shocking the pool several times but just can't get rid of it. Is it possible to get rid of black algae in a painted pool?

Thanks.

[quantumchromodynamics]

If the black is coming from the underside of the paint, it's not algae. It could be some sort of ground contaminant, such as oil, seeping through the gunite and staining the paint.

[Gavin]

If the black is coming from the underside of the paint, it's not algae. It could be some sort of ground contaminant, such as oil, seeping through the gunite and staining the paint.

it only turned black when I added chlorine. when I added a good amount of bleach direct to the step area where some of the black algae is it went away. but it keeps coming back.

[quantumchromodynamics]

If it turned black when you added chlorine, then it is not algae.

Black stains can happen when you shock with calcium hypochlorite and the pH and/or the alkalinity are low.

I'm not sure what the black is; it might be a metal oxide, such as from copper.

What are your pH and alkalinity?

What did you use to shock the pool?

Is there any copper in the water?

[Gavin]

If it turned black when you added chlorine, then it is not algae.

Black stains can happen when you shock with calcium hypochlorite and the pH and/or the alkalinity are low.

I'm not sure what the black is; it might be a metal oxide, such as from copper.

What are your pH and alkalinity?

What did you use to shock the pool?

Is there any copper in the water?

oh thanks. ph is good 7.4 but I've never been able to get a reading on the TA. I have a cheap test kit. I've been trying to get a Taylor kit in. I live in the Caribbean but the stores just sell Guardex kits.

I don't have anything to test for copper. One time I was filling up the pool and had the pump off. I added a couple cases of bleach thinking that would get rid of the black but it just made the pool water black. When I looked closer to the water I could see bits of black stuff floating in the water. could this be metals or copper in the water? my DE filter did eventually clear the water up but the black on the floor and walls were still there.

[quantumchromodynamics]

My best guess would be copper II Oxide.

I would be concerned about not being able to get an alkalinity reading. That is a very important number to know. What happens when you do the alkalinity test?

Does the pool have a heater?

Are there any other stains of any kind, especially green stains?

What are all of your other chemical readings?

[Gavin]

My best guess would be copper II Oxide.

I would be concerned about not being able to get an alkalinity reading. That is a very important number to know. What happens when you do the alkalinity test?

Does the pool have a heater?

Are there any other stains of any kind, especially green stains?

What are all of your other chemical readings?

Thanks for all you help! very much appreciated. I did a test with a chlorine tablet. left it over night and checked it today. underneath it was still black so can't be organic. in fact there was even a slight color of purple under the tablet. so like you said it is metal reaction with chlorine.

The pool does have a heater but it's never turned on.

The alkalinity test is very hard to read but when I add the die I do see some faint blue type color. when I added drops last time I think the TA was between 120-140. but the chlorine level was high so they say readings might not be accurate. I think thats how this test kit is. the TA is very hard to read. the color change is very hard to see. but I did a test twice and it read 120 and then 140. but like I said its very hard to see the change to clear.

ph seems to be able to be adjusted no problems so TA buffering must be ok. like 120-140? I'm assuming.

chlorine is high since I just shocked it. again can't say how high as the test kit is not a FAS-DPD. Its just OTO.

I'm seeing just a couple small spots that seem greenish. but nothing like the black. some green around the tile grout and I think I see a green patch by the steps.

[Pool Clown]

Can you get some of this "black stuff" in your hands to feel if it is slimy? Black algae is tough to get rid of. Alot of times, chlorine wont touch it unless you can "knock the heads off the blooms first". You usually have to use a algaecide specifically for black algae (you'll probably have to get it online, given where you are). One of the reasons its so tough is because B/A likes to get into cracks or porous places where it can get a strong foothold.

If you had B/A before the pool was painted and didn't get all of it off before painting, it could very possibly be coming through the paint.

[Gavin]

Can you get some of this "black stuff" in your hands to feel if it is slimy? Black algae is tough to get rid of. Alot of times, chlorine wont touch it unless you can "knock the heads off the blooms first". You usually have to use a algaecide specifically for black algae (you'll probably have to get it online, given where you are). One of the reasons its so tough is because B/A likes to get into cracks or porous places where it can get a strong foothold.

If you had B/A before the pool was painted and didn't get all of it off before painting, it could very possibly be coming through the paint.

Thanks for the reply. yes this is what I thought was happening but I've been brushing and brushing and shocking and shocking and it doesn't go away. I rubbed the black with my hands but it wasn't slimy. and I left a chlorine puck on the black overnight and found no change but a slight purple color underneath the puck.

I just read this online: "Manganese will result in dark brownish/black or purple stains."

could that purple color under the puck be a sign of Manganese? but where would that come from?

some additional info: it is a painted pool. the previous owner painted with the same paint they used on the house. you can see where they rolled the paint on. some parts are darker than others and the visible roll lighter. the black shows roll marks from when they painted. maybe some parts had an extra coat of paint? I still think it must be metals. maybe copper from the old rusty pool heater. and there is no check valve to bypass the heater.

[Pool Clown]

Not sure. Why did the pool get painted? Were you getting the same thing before you painted?

[Gavin]

Not sure. Why did the pool get painted? Were you getting the same thing before you painted?

don't know previous owners painted the pool with the same paint they used on the house.

[Pool Clown]

Unless the "house" was a boat, it was the wrong paint for a pool! There could be something going on with the paint that is doing this. I personally don't like to "recommend" to paint pools. It is hard to do it correctly (mostly prep) and even if you do it correctly, there is a possibility that you will develop problems, and then, what do you do next?

Recommendation? Wow, thats hard. How much time/MONEY are you willing to give this?

To repaint, you gotta drain, blast (sand), and redo with correct coating.

To do correctly (bias opinion) drain, blast ALL of it off, bond coat, and re-plaster.

Live with it? Ugliest of choices. Actually, not having seen your pool, "ugliest" is probably not the right description, but you get the idea.

[Gavin]

Unless the "house" was a boat, it was the wrong paint for a pool! There could be something going on with the paint that is doing this. I personally don't like to "recommend" to paint pools. It is hard to do it correctly (mostly prep) and even if you do it correctly, there is a possibility that you will develop problems, and then, what do you do next?

Recommendation? Wow, thats hard. How much time/MONEY are you willing to give this?

To repaint, you gotta drain, blast (sand), and redo with correct coating.

To do correctly (bias opinion) drain, blast ALL of it off, bond coat, and re-plaster.

Live with it? Ugliest of choices. Actually, not having seen your pool, "ugliest" is probably not the right description, but you get the idea.

Thanks so if I went with either solution I would still need to stop the metals going into the pool. It might be copper from the heat exchanger of the pool heater. I guess I could bypass the heater to prevent this staining from happening again? if it is copper from corroded heat exchanger.

[Pool Clown]

Unless the "house" was a boat, it was the wrong paint for a pool! There could be something going on with the paint that is doing this. I personally don't like to "recommend" to paint pools. It is hard to do it correctly (mostly prep) and even if you do it correctly, there is a possibility that you will develop problems, and then, what do you do next?

Recommendation? Wow, thats hard. How much time/MONEY are you willing to give this?

To repaint, you gotta drain, blast (sand), and redo with correct coating.

To do correctly (bias opinion) drain, blast ALL of it off, bond coat, and re-plaster.

Live with it? Ugliest of choices. Actually, not having seen your pool, "ugliest" is probably not the right description, but you get the idea.

Thanks so if I went with either solution I would still need to stop the metals going into the pool. It might be copper from the heat exchanger of the pool heater. I guess I could bypass the heater to prevent this staining from happening again? if it is copper from corroded heat exchanger.

When copper is getting eroded from a heat exchanger, it will usually result in a turquoise colored stain in the pool. I don't think this is comming from your heat exchanger.

[Gavin]

Unless the "house" was a boat, it was the wrong paint for a pool! There could be something going on with the paint that is doing this. I personally don't like to "recommend" to paint pools. It is hard to do it correctly (mostly prep) and even if you do it correctly, there is a possibility that you will develop problems, and then, what do you do next?

Recommendation? Wow, thats hard. How much time/MONEY are you willing to give this?

To repaint, you gotta drain, blast (sand), and redo with correct coating.

To do correctly (bias opinion) drain, blast ALL of it off, bond coat, and re-plaster.

Live with it? Ugliest of choices. Actually, not having seen your pool, "ugliest" is probably not the right description, but you get the idea.

Thanks so if I went with either solution I would still need to stop the metals going into the pool. It might be copper from the heat exchanger of the pool heater. I guess I could bypass the heater to prevent this staining from happening again? if it is copper from corroded heat exchanger.

When copper is getting eroded from a heat exchanger, it will usually result in a turquoise colored stain in the pool. I don't think this is comming from your heat exchanger.

oh ok. thanks. but where? I am slightly color blind btw.

[quantumchromodynamics]

Copper stains are usually turquoise, but they can also be other colors depending on what oxidation state the copper is in and what it is combining with.

Copper II oxide is black, and copper cyanurate is purple. Hydrated copper sulfate and hydrated copper carbonate are both green.

Copper that is eroded is in the solid, unoxidized state. However, it can be oxidized by chlorine, at which point it can combine with other elements and stain.

How do you add the trichlor tabs?

What is your cyanuric acid level?

It could be manganese or copper. Can you have the water tested for copper and manganese?

[Pool Clown]

Depending on the surface of the plaster at the time, it can be anything from blotchy to uniform throughout the pool.

[Gavin]

Copper stains are usually turquoise, but they can also be other colors depending on what oxidation state the copper is in and what it is combining with.

Copper II oxide is black, and copper cyanurate is purple. Hydrated copper sulfate and hydrated copper carbonate are both green.

Copper that is eroded is in the solid, unoxidized state. However, it can be oxidized by chlorine, at which point it can combine with other elements and stain.

How do you add the trichlor tabs?

What is your cyanuric acid level?

It could be manganese or copper. Can you have the water tested for copper and manganese?

I used to add the tabs to the skimmer but I read it's better to use a floater so I'm using that now.

I am unable to test for cyanuric acid right now but I did drain the pool by 50% and refill. I though the stabilized level might be too high and it rendered the chlorine ineffective so I drained the pool by 50% and refilled.

Yes I can test it in a lab here but they charge $50 per metal.

[Gavin]

Depending on the surface of the plaster at the time, it can be anything from blotchy to uniform throughout the pool.

Yes this is what is happening.

Btw guys thanks so much for the info it is very helpful.

[quantumchromodynamics]

Using trichlor tabs in a skimmer will definitely cause the heat exchanger to be damaged as the copper is corroded.

I think this is most likely being caused by copper and that the heat exchanger is the most likely source of copper.

Have you ever used a copper or silver based algaecide or any type of ionizer?

The purple is probably copper cyanurate. If there was copper on, or in, the paint, the chlorine in the tab would oxidize the copper and the copper could then combine with the cyanurate in the trichlor tab.

[quantumchromodynamics]

I think that it's probably worthwhile to have the lab test for copper and manganese just to be sure. That way we will know what we are dealing with and can handle it more effectively.

Get some vitamin C tabs, crush then up into a powder and then put the powder on some of the stains. Allow the Vitamin C to sit for a while to see if it will remove the stain.

If that works, you could do an ascorbic acid treatment to remove the stains. Then you could use a metal chelator/sequestrant to help prevent further metal problems.

Ideally, you would want to remove the metals from the water to prevent future problems.

[Gavin]

I think that it's probably worthwhile to have the lab test for copper and manganese just to be sure. That way we will know what we are dealing with and can handle it more effectively.

Get some vitamin C tabs, crush then up into a powder and then put the powder on some of the stains. Allow the Vitamin C to sit for a while to see if it will remove the stain.

If that works, you could do an ascorbic acid treatment to remove the stains. Then you could use a metal chelator/sequestrant to help prevent further metal problems.

Ideally, you would want to remove the metals from the water to prevent future problems.

Thanks that make sense. I was thinking about doing that. I can get it tested at the lab. and then try the ascorbic acid vit C to see if it removes the stain then treat with an ascorbic acid treatment. also I want to bypass the heater to prevent anymore problems.

[quantumchromodynamics]

Go ahead and try the vitamin C test now. It's a quick and easy way to test for metal stains.

[Gavin]

Go ahead and try the vitamin C test now. It's a quick and easy way to test for metal stains.

will definitely do that. many thanks!

[Gavin]

tried the ascorbic acid Vit C test. will leave it over night and check results in the morning.

I got my new test kit the other day and did some test and these are my readings:

FC=50

CC=0

pH=7.0 (Base Demand=4)

TA=60-90 avg:75

CH=100

CYA=-30

I need to buy a thermometer now to get water temp.