Swimming Pool - Black Dots Appearing !

[Carlosm]

My swimming pool has suddenly started to get these 1" wide solid black marks appearing all over. I've done the water test and its the same as always. They are smooth dome shaped and can only be removed by chiseling them off.

Does anyone know of a chemical solution that will remove these dots and why they've suddenly started to appear ?

[bkkjames]

Check in the do it yourself housing forum, I think there are some swimming pool topics.

Black dots appearing in your pool? Strange, very very strange this is.

[samuibeachcomber]

For correct advice should go to a swimming pool supplier.From memory its a build up of calcium deposits.The black dots usually means funghi is attaching itself to the calcium even though the ph readings are correct.

[CHdiver]

TV has a Swimming Pool Forum (go figure), maybe a Mod will move you question there?

[PoolDoctor]

? This is the swimming pool forum no?

Hi,

Without seeing any pictures, I am going to go out on a limb and assume that you are getting some black algae in the pool. Attaching example picture here. This is reinforced by your comment that they can be removed by chiseling (there are steel algae brushes avail). Black algae must be treated in two ways - chemically, and brute force. First thing - check your pH, and drop your pH to 7.0. This is slightly acidic, but it boosts the efficiency of chlorine upwards greatly. 2nd, check free chlorine digitally, or more accurately, check ORP and keep it above 600 (lots info on the 'net regarding ORP). Don't waste your time with DPD or OPD testing kits, regents, etc., just get yourself a decent handheld pH and ORP tester. It will pay for itself time and time again.

Finally, treat the pool with a black algae-cide as per directions. While doing this, you must brush the pool vigorously - black algae covers itself in a protective hard shell which must be penetrated first for the chemicals to seep in and do their work. Likely, black algae has taken hold during the rainy season, and you have allowed ORP or free chlorine levels to drop too far. Or, at a similar ORP level, your pH has risen (high pH inhibits oxidation power of chlorine - at 8.0 pH I think efficiency of chlorine drops to like 15% or something like that).

Is your pool a salt or chlorine system? If its a salt system, do you have enough cyuranic acid in the water?

[WormFarmer]

? This is the swimming pool forum no?

Hi,

Without seeing any pictures, I am going to go out on a limb and assume that you are getting some black algae in the pool. Attaching example picture here. This is reinforced by your comment that they can be removed by chiseling (there are steel algae brushes avail). Black algae must be treated in two ways - chemically, and brute force. First thing - check your pH, and drop your pH to 7.0. This is slightly acidic, but it boosts the efficiency of chlorine upwards greatly. 2nd, check free chlorine digitally, or more accurately, check ORP and keep it above 600 (lots info on the 'net regarding ORP). Don't waste your time with DPD or OPD testing kits, regents, etc., just get yourself a decent handheld pH and ORP tester. It will pay for itself time and time again.

Finally, treat the pool with a black algae-cide as per directions. While doing this, you must brush the pool vigorously - black algae covers itself in a protective hard shell which must be penetrated first for the chemicals to seep in and do their work. Likely, black algae has taken hold during the rainy season, and you have allowed ORP or free chlorine levels to drop too far. Or, at a similar ORP level, your pH has risen (high pH inhibits oxidation power of chlorine - at 8.0 pH I think efficiency of chlorine drops to like 15% or something like that).

Is your pool a salt or chlorine system? If its a salt system, do you have enough cyuranic acid in the water?

Hi PD.

I have a fairly new salt water pool in Roi Et and am just learning about how to maintain it. Recently we too have noticed some small black dots similar to those described above which we have been scraping off. I do have a gallon of black algeacide but haven't used it yet. Recently the water has been very warm so this could be affecting free chlorine content. You mention the need to measure this and / or ORP. My questions are: What is ORP and how / where do I buy a decent handheld pH and ORP tester. Also where, and in what form, can I buy cyuranic acid to stabilise the chlorine content?

[craigt3365]

Dang, I just started getting these also...but they seems to be "inside" the tile. I tried to clean them off by scraping them, but they are flat with the surface...can't feel anything. Tried using a brush and my finger nails. No luck. They were not there 3 days ago, now starting to appear everywhere!

[spshop]

If you guys have clay tiles the problem is RUST the grade B-C tiles have ironoxide in the colour and after a while water seeps in and the rust starts. No way to fix this other than replacing the tile.

Dang, I just started getting these also...but they seems to be "inside" the tile. I tried to clean them off by scraping them, but they are flat with the surface...can't feel anything. Tried using a brush and my finger nails. No luck. They were not there 3 days ago, now starting to appear everywhere!

[WormFarmer]

If you guys have clay tiles the problem is RUST the grade B-C tiles have ironoxide in the colour and after a while water seeps in and the rust starts. No way to fix this other than replacing the tile.

Thanks for the thought spshop, but no clay tiles here, best quality crystal pool tiles, see photos taken shortly after completion a month or so back. So I'm still looking for a source, in LOS, of a decent handheld pH and ORP tester as recommended by PoolDoctor, any suggestions anybody?

[craigt3365]

If you guys have clay tiles the problem is RUST the grade B-C tiles have ironoxide in the colour and after a while water seeps in and the rust starts. No way to fix this other than replacing the tile.

Thanks for the thought spshop, but no clay tiles here, best quality crystal pool tiles, see photos taken shortly after completion a month or so back. So I'm still looking for a source, in LOS, of a decent handheld pH and ORP tester as recommended by PoolDoctor, any suggestions anybody?

Nice pool. Love those big trees behind you!

Regarding tiles, I am in the same spot. Glazed pool tiles like yours...but some with black spots!

[PoolDoctor]

Hi, we carry both the testors (ph & ORP) and cyuranic. All on our site.

Best,

Gil

? This is the swimming pool forum no?

Hi,

Without seeing any pictures, I am going to go out on a limb and assume that you are getting some black algae in the pool. Attaching example picture here. This is reinforced by your comment that they can be removed by chiseling (there are steel algae brushes avail). Black algae must be treated in two ways - chemically, and brute force. First thing - check your pH, and drop your pH to 7.0. This is slightly acidic, but it boosts the efficiency of chlorine upwards greatly. 2nd, check free chlorine digitally, or more accurately, check ORP and keep it above 600 (lots info on the 'net regarding ORP). Don't waste your time with DPD or OPD testing kits, regents, etc., just get yourself a decent handheld pH and ORP tester. It will pay for itself time and time again.

Finally, treat the pool with a black algae-cide as per directions. While doing this, you must brush the pool vigorously - black algae covers itself in a protective hard shell which must be penetrated first for the chemicals to seep in and do their work. Likely, black algae has taken hold during the rainy season, and you have allowed ORP or free chlorine levels to drop too far. Or, at a similar ORP level, your pH has risen (high pH inhibits oxidation power of chlorine - at 8.0 pH I think efficiency of chlorine drops to like 15% or something like that).

Is your pool a salt or chlorine system? If its a salt system, do you have enough cyuranic acid in the water?

Hi PD.

I have a fairly new salt water pool in Roi Et and am just learning about how to maintain it. Recently we too have noticed some small black dots similar to those described above which we have been scraping off. I do have a gallon of black algeacide but haven't used it yet. Recently the water has been very warm so this could be affecting free chlorine content. You mention the need to measure this and / or ORP. My questions are: What is ORP and how / where do I buy a decent handheld pH and ORP tester. Also where, and in what form, can I buy cyuranic acid to stabilise the chlorine content?

[WormFarmer]

Hi, we carry both the testors (ph & ORP) and cyuranic. All on our site.

Best,

Gil

Hi PD,

Thanks for that, I also got your PM with your site address and have replied - I'll be contacting you for my needs.

WF