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Comment
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.
Congratulations for getting some credit for your work on CYA in Service Industry News ! !
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.
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?
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.
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.
Hi Richard:
Please, I am requesting update information about ORP in Swimming pools.
THKS IN ADVANCE
N/B: MY eMAIL IS areadepiscinas@gmail.com
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