Black algae in a watersalted swimming pool

[janclaes47]

20 minutes ago, Spellforce said:

- "Total Hardness"; as long you didn't use a lot of chemical products, your water wont be "hard"

- Free Chlorine: as long as you pH is low and even a little acid in a tropical country as Thailand (pH < 7), then the "Total Chlrorine" indicator is enough

- Total alkalinity = Total hardness

- pH never more than 7.2 -7.3

- "Cyanuric acid": for what ? When you have a salted SP you don't need to use a lot of acids, so the CYA is always low

 

What I"ve read yesterday is that black algaes like salted SP and that the "free chlorine" wont kill those algaes. Only copper sulfate can kill those algaes but dont use it too much or you will have green hairs :)

 

Never seen so many wrongs in one single post.

 

Good luck

[grollies]

1 hour ago, Spellforce said:

- "Total Hardness"; as long you didn't use a lot of chemical products, your water wont be "hard"

- Free Chlorine: as long as you pH is low and even a little acid in a tropical country as Thailand (pH < 7), then the "Total Chlrorine" indicator is enough

No, you need to be measuring free chlorine.

 

Quote

- Total alkalinity = Total hardness

Nope

 

Quote

- pH never more than 7.2 -7.3

Debateable, people have different opinions, I'm happy at around 7.8

 

Quote

- "Cyanuric acid": for what ? When you have a salted SP you don't need to use a lot of acids,

Yes you do, OK, not lots but you should have an acid dosing system linked to your chlorinator on a 100m3+ pool.

 

Quote

 

so the CYA is always low

Cyanuric acid is a pH stabilizer 

Quote

 

What I"ve read yesterday is that black algaes like salted SP and that the "free chlorine" wont kill those algaes.

True free chlorine will not kill black algae once it is established. The ONLY way to get rid of black algae is to brush, circulate, filter (with the aid of the black algae treatment containing a flocculant) and repeat until it's all gone. BUT sufficient FREE chlorine in your pool will kill black algae spores and prevent them gathering in your tile grout.

 

Quote

 

Only copper sulfate can kill those algaes but dont use it too much or you will have green hairs :)

Like I and many others above have said, get your pool water balanced. I haven't added anything but acid via dosing pump (to keep the pool water pH level, if you don't add then your pH will gradually increase).

 

You tell us your pH, etc but NEVER mention FREE chlorine levels. Get a better test kit?

[janclaes47]

2 minutes ago, grollies said:

Quote

 

so the CYA is always low

Cyanuric acid is a pH stabilizer 

 

Cyanuric acid is a chlorine stabilizer, and is needed in a tropical country to avoid getting the chlorine depleted too fast from the UV.

 

With the OP's current pH of 6.8 he will not even be able to measure CYA

4 minutes ago, grollies said:

Quote

- "Cyanuric acid": for what ? When you have a salted SP you don't need to use a lot of acids,

Yes you do, OK, not lots but you should have an acid dosing system linked to your chlorinator on a 100m3+ pool.

 

Cyanuric acid doesn't get dosed, and is not connected to the chlorinator, muriatic acid is dosed and can be connected to the chlorinator to keep pH at the desired level.

 

Cyanuric acid, once it is in the water it stays, and can only be lowered by diluting

[grollies]

2 hours ago, janclaes47 said:

 

Cyanuric acid is a chlorine stabilizer, and is needed in a tropical country to avoid getting the chlorine depleted too fast from the UV

Sorry, yes, meant Cl not pH.

 

2 hours ago, janclaes47 said:

 

With the OP's current pH of 6.8 he will not even be able to measure CYA

 

Cyanuric acid doesn't get dosed, and is not connected to the chlorinator, muriatic acid is dosed and can be connected to the chlorinator to keep pH at the desired level.

I dose dilute hydrochloric acid not cyanuric acid to control pH. Dosed from the chlorinator algorithm output.

 

pH stable although a little high.

 

I manually added cyanuric acid two months ago to 40ppm. I hadn't done this before which is why I had problems with my free Cl (or lack of it)-leading to black algae problems.

 

Free Cl is now OK at 3ppm, chlorinator working much better.

 

2 hours ago, janclaes47 said:

 

Cyanuric acid, once it is in the water it stays, and can only be lowered by diluting

Agree.

 

Sorry for the confusion.

[sappersrest]

 

janclaes47/

"With the OP's current pH of 6.8 he will not even be able to measure CYA."

Whilst in the quest for knowledge could you please point me in the right direction to clarify this statement i.e. scientific paper or other source.

Many thanks

[janclaes47]

28 minutes ago, sappersrest said:

 

janclaes47/

"With the OP's current pH of 6.8 he will not even be able to measure CYA."

Whilst in the quest for knowledge could you please point me in the right direction to clarify this statement i.e. scientific paper or other source.

Many thanks

To start with it is written on every Aquachek test strip container, and I doubt they write that without a reason

Second reason for my comment you can read here

 

https://www.troublefreepool.com/threads/94961-Does-pH-affect-CYA-measurement?p=816841&viewfull=1#post816841

 

"If Bioguard uses a CYA test that does not have a strong acid buffer in it, then the melamine-CYA complex may not form if the pH is high which it may very well be after the biodegradation of CYA. In fact, at a pH of 7, the melamine-CYA complex is soluble up to 20 ppm. The Taylor test has an acid buffer in its melamine reagent to maximize precipitation in the CYA test giving accurate results (otherwise, they'd never be able to measure down to 20 ppm). So I think you hit the nail on the head in thinking that the Bioguard CYA test tablet is a poor test reagent that is inaccurate under conditions of a pH out of normal range (especially high pH). "

 

Third reason for my comment.

 

I recall testing the pool from my ex who had been using Trichlorine in large amount for more than a year, so I suspected a high CYA.

 

I tested on a certain day with my Aquachek silver strips, and CYA measured as 0, but pH was also not measurable. ( less than 6.2 )

 

In the next few days I brought the pH up to a level around 7.0 - 7.4 and the CYA then measured OVER 300 ppm.

 

Edit to add : It is clear from the OP's posts that he uses a 2 tube test kit. With such a kit he will even be unable to distinguish between a 6.8 and a 6.5 or lower reading of his pH

Edited September 28, 2017 by janclaes47

[sappersrest]

 

Interesting  it would seem that that the reagents used play a big part in the result depending on pH.

 I use a plainest photometer and have not come across this anomaly but have had some spurious readings using test strips.

Thanks for the heads up will contact  a few  reagent companies and chemists that I know and will report back,

Thanks for your input as it raises some very important points.

Edited September 28, 2017 by sappersrest

[janclaes47]

5 minutes ago, sappersrest said:

 

Interesting  it would seem that that the reagents used play a big part in the result depending on pH.

 I use a plainest photometer and have not come across this anomaly but have had some spurious readings using test strips.

Thanks for the heads up will contact  a few  reagent companies and chemists that I know and will report back,

Thanks for your input as it raises some very important points.

 My comment was primarily in regard to test strips, and from the post on Troublefree pool it states that a Taylor test has the pH buffers added, but you will have a hard time to find a Taylor test kit in Thailand that tests for all those chemicals. And if you find one you will have to sell your car to afford it :-)

[mindovermatter]

Have encountered this problem too back in January. The algaecide from PoolMaster has remarkably solved it. I've tried ordering one from eBay and good thing I didn't as I wanted a local pool supplier so I can contact them anytime through phone. You may find this link useful: Black Advance Algaecide  Hope this helps! 

[Bagwain]

1st and foremost - if the water is kept in balance black (spot) algae shouldn't happen. Basics . ph range 7.2 - 7.8, T/A 80 - 120, calcium hardness 250 - 300. Black spot is a result of long periods of high ph. It is a flower with roots. If you just brush the heads off they will come back as the roots are still in the grout. Cl is ineffective against it. The simplest way is to drop your ph to way below 7 and use the black algaecide mention in previous replies. (The algaecide is not potent with ph over 7) circulate for an hr and shut the pool down for 24 hrs. This should kill the roots and all. Brush and let settle for another 12 hrs and then vacuum. If your pool is small enough I would vacuum to waste. If not do a backwash as soon as vacuuming is finished.

 

For everyone's info - it is inadvisable to use copper sulfate with salt chlorination pools. You may jeopardise your warranty. If you do use it no more than .3 ppm. Only good for green algae. Black & mustard algae are 2 completely different beasts.