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Water Chemistry

This group is for in-depth discussion of pool and spa water chemistry issues at a more technical level suitable to a group for those who are interested.  The emphasis is on matching science and research to real-world observations.

Members: 75
Latest Activity: Feb 12

Discussion Forum

Cyanuric Acid for Indoor Pools? 3 Replies

Started by Howard J Knight. Last reply by Jory Jan 19, 2017.

flocculant 8 Replies

Started by Frank H Dashti. Last reply by Roohollah Akbari Jun 21, 2016.

Phosphates, Phosphate Removers and CuLator™ Metal Remover 57 Replies

Started by Richard A. Falk. Last reply by Richard A. Falk Apr 24, 2013.

Combined Chlorine-what is it exactly? 6 Replies

Started by David Rockwell. Last reply by Richard A. Falk Dec 29, 2012.

The mysterious case of the disappearing CYA 7 Replies

Started by David Rockwell. Last reply by Rick Larson Oct 10, 2012.

Natural Swimming Pools (NSPs) 1 Reply

Started by Richard A. Falk. Last reply by John Pustai Jul 27, 2012.

Enzymes 18 Replies

Started by Richard A. Falk. Last reply by Aaron Heiss Jul 5, 2012.

Oxidation-Reduction Potential (ORP) 6 Replies

Started by Richard A. Falk. Last reply by Richard A. Falk Jun 11, 2012.

Breakpoint Chlorination 4 Replies

Started by Richard A. Falk. Last reply by Richard A. Falk May 29, 2012.

CYA, TA, and the Langelier Index 1 Reply

Started by David Rockwell. Last reply by Richard A. Falk Feb 12, 2012.

SWG and borates 5 Replies

Started by Jeremy Hine. Last reply by Richard A. Falk Dec 4, 2011.

Air Quality Above Pool/Spa Water 3 Replies

Started by Richard A. Falk. Last reply by Richard A. Falk Nov 17, 2011.

Biofilms 28 Replies

Started by Richard A. Falk. Last reply by Richard A. Falk Jul 12, 2011.

Algae 3 Replies

Started by Richard A. Falk. Last reply by Richard A. Falk Jun 9, 2011.

Chlorine Dioxide 2 Replies

Started by Richard A. Falk. Last reply by Richard A. Falk Apr 8, 2011.

Total Dissolved Solids (TDS) 6 Replies

Started by Richard A. Falk. Last reply by Richard A. Falk Mar 19, 2011.

Active Chlorine Level and Disinfection By-Products (DBPs) 14 Replies

Started by Richard A. Falk. Last reply by Richard A. Falk Mar 10, 2011.

Lowering Total Alkalinity (TA) 5 Replies

Started by Richard A. Falk. Last reply by Richard A. Falk Feb 23, 2011.

Total Alkalinity (TA) and pH Effects 1 Reply

Started by Richard A. Falk. Last reply by Richard A. Falk Feb 21, 2011.

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Comment by Richard A. Falk on February 12, 2019 at 9:23pm

Thanks Lester.  This is actually the second time they ran the article describing the history of the chlorine/CYA relationship and my role in disseminating it.  The one thing they don't describe is that the 7.5% minimum FC/CYA ratio is for preventing green and black algae growth regardless of phosphate level.  If one controls phosphates (particularly to < 500 ppb) then one can use a lower ratio of 3-4% and can also more easily control yellow/mustard algae that with high phosphate and nitrate levels can need up to 15% FC/CYA ratio to control.

Comment by Lester Eric Brehm on February 12, 2019 at 12:27pm

Congratulations for getting some credit for your work on CYA in Service Industry News ! !

Comment by Richard A. Falk on October 25, 2012 at 10:13am

Yes, as Al points out, algae growth indicates a problem with your chlorine level.  Black algae grows slowly so would indicate a prolonged problem, not just having the chlorine too low for a few days, but rather for weeks or months.  Since green algae usually shows up first and more quickly, I suspect you've got a problem with poor circulation in the areas where the black algae is growing.  See the discussion on algae.

Is this aquatic centre indoors or outdoors exposed to sunlight?  What kind of chlorine are you using and at what Free Chlorine (FC) level?  Is there Cyanuric Acid (CYA), aka stabilizer or conditioner, in the water and if so at what level?  See the discussion on the Chlorine / Cyanuric Acid (CYA) Relationship.

You can get rid of black algae by maintaining a somewhat higher chlorine level AND most importantly brushing with a strong brush to knock off the outer slimy layer of the algae to expose depths to high chlorine.  Some people use Trichlor pucks or powder directly on the spot, but this can leave a mark on pool surfaces (and you can only do this with plaster and not with vinyl).  Since the problem is probably related to poor circulation, you should look at directing some of your returns in a way to provide better bottom circulation (assuming the algae is at the bottom) though this will reduce surface circulation to skimmers/gutters.

As for using carbon dioxide for pH control, it's a very lame way to control the pH because it means that you are just putting carbon dioxide back into a pool that is outgassing it.  If the pH tends to rise if you don't try and adjust it, then this means that your Total Alkalinity (TA) is too high and that the rise is due to carbon dioxide outgassing.  You will ironically get more pH stability with a lower TA in this situation.  What is your current TA level?  See the discussion Total Alkalinity (TA) and pH Effects and Lowering Total Alkalinity and the pH of Chlorine Sources.

Comment by Al Neumann on October 25, 2012 at 9:19am
Howard,
Black Algae is an issue that deals with the effectiveness of your chlorine, and I suspect that chlorine isn't keeping up with demand at some point. CO2 and pH would be an issue if pH levels were higher than normal. I'm sure Richard will point you to a lot of discussions on this topic. For starts, just browse down to the algae discussions in this group.
You might also want to consider on the new facility to take a look at SureWaters HCF Liquid Chlorine Venturi Feeder as a means of keeping up with demand more easily.
http://www.sureh2o.com/
Comment by Howard J Knight on October 25, 2012 at 8:54am

Yes, we have a company telling us we have black algae.  In my conversation with our Manager she changed it to mold.  I looked over the report for myself and it states Black algae, any ideas?

Comment by Al Neumann on October 25, 2012 at 8:49am
Howard,
Just curious on the "black mold" issue. Is this an actual mold, or a black algae issue?
Comment by Howard J Knight on October 25, 2012 at 8:05am

Richard,   Our new aquatic centre is getting built and the question of Carbon Dioxide controlling pH is being made.  Have you or anyone else found the problem of 'Black mold" with CO 2 systems?  We use approxiatmately 500 lbs of CO2 each month, with a 140,000 gallon pool system.

 

Comment by Richard A. Falk on June 7, 2012 at 2:04pm

That's a good discussion suggestion.  I'll work on that, but in the meantime you can take a look at this post and this post that show how ridiculous it is to use ORP as an absolute measure since there is so much inconsistency between different manufacturer's units even measuring the same pool water.  ORP is fine for process control if you correlate a target FC level against an ORP level.

Comment by Hugo Diaz on June 7, 2012 at 1:11pm

Hi Richard:

Please, I am requesting update information about ORP in Swimming pools.

THKS IN ADVANCE

N/B: MY eMAIL IS areadepiscinas@gmail.com

Comment by Richard A. Falk on August 10, 2011 at 5:37pm
OK, I've added a discussion for that (note that you can do that yourself in the future if you want).  As for cyanogen chloride, let me know if you have Blatchley's papers on the subject as this is part of what he was measuring using MIMS for measurement.  I'll add some links and info to the discussion topic now.
 

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