I wanted to know what the basis for the slam level fc is? And what is the equation used in determine slam level considering all other variables (cya etc..) just kinda curious about it. It is the best remedy by far!
Slam level basis?
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Where did the slam target come from? Is there a general equation used to determine this?
- Jun 24, 2021
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Chlorine/CYA Chart
EDIT: You will find a simplified and standardized version of this chart at Pool School, Chlorine / CYA Chart. Chlorine/CYA Chart by Chemgeek FC = Free Chlorine in parts-per-million (ppm) CYA = Cyanuric Acid in parts-per-million (ppm) CYA ........... Min FC3 ..... Target FC ...... Yel/Mstrd...
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Thanks for the response. I am wondering the basis of the chart. Where did the values in the chart come from?Chlorine/CYA Chart
EDIT: You will find a simplified and standardized version of this chart at Pool School, Chlorine / CYA Chart. Chlorine/CYA Chart by Chemgeek FC = Free Chlorine in parts-per-million (ppm) CYA = Cyanuric Acid in parts-per-million (ppm) CYA ........... Min FC3 ..... Target FC ...... Yel/Mstrd...
- Jun 24, 2021
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The last paragraph in the first post of the thread I gave you...with links to Ben's original and link to the pool forum.
ACKNOWLEDGMENT: The original chlorine/CYA chart was developed by Ben Powell and is shown here based mostly on experience plus some conversations with chemists. With the help of users at The Pool Forum and this forum, we expanded the chart to include yellow/mustard algae and I made the chart consistent with chemical theory.
More on the chemistry...
Pool Water Chemistry
This thread presents my findings so far on pool water chemistry including the following: More Accurate Calcite Saturation Index (CSI) to replace Langelier Saturation Index (LSI) Calculation of ppm HOCl (disinfecting chlorine) at various levels of Total Free Chlorine (FC) and Cyanuric Acid (CYA)...
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- May 23, 2015
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Shock level for TFP is 40% of the CYA value. That roughly gives a little over 1 to 1.5ppm hypochlorous acid (HOCl) concentration which is the primary disinfectant and oxidizer for chlorine. 1ppm HOCl is about 20X the concentration of HOCl at the standard target FC levels.
There’s nothing magical or scientific about the 40% value. It’s simply a trade off between safety (of equipment and surfaces), rate of clearance, and efficient use of liquid chlorine, which is not cheap these days. Pool service companies have been known to shock pools at much higher levels (100% of CYA) to clear a pool fast but that is very dangerous and could easily bleach out a pool surface. The government regulators will ignore CYA and call anything over 10ppm FC “shock”.
There’s nothing magical or scientific about the 40% value. It’s simply a trade off between safety (of equipment and surfaces), rate of clearance, and efficient use of liquid chlorine, which is not cheap these days. Pool service companies have been known to shock pools at much higher levels (100% of CYA) to clear a pool fast but that is very dangerous and could easily bleach out a pool surface. The government regulators will ignore CYA and call anything over 10ppm FC “shock”.
- Mar 5, 2020
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Was just typing my reply when Matt's post popped up. Posting it anyway, mostly just confirming what Matt said in other words...
Solving the involved chemical equilibrium equations (for example with Chem Geek's Pool equations spreadsheet) shows that same ratios of FC/CYA yield the same amounts of HOCl, which is actual sanitising chlorine "species", and over the pool relevant pH-range, pH-dependancy is small.
SLAM level is an FC/CYA ratio of 40%, equivalent to an HOCl concentration of about 0.32ppm (that would be FC=0.64ppm at pH 7.5 without CYA in the water). This has been chosen as a good compromise between algae killing times and keeping the water swimmable, not damaging the equipment and reasonable amounts of chlorine to be added.
Higher levels would burn off very quickly under UV anyway, and you'd be topping up chlorine constantly to maintain slam level.
Solving the involved chemical equilibrium equations (for example with Chem Geek's Pool equations spreadsheet) shows that same ratios of FC/CYA yield the same amounts of HOCl, which is actual sanitising chlorine "species", and over the pool relevant pH-range, pH-dependancy is small.
SLAM level is an FC/CYA ratio of 40%, equivalent to an HOCl concentration of about 0.32ppm (that would be FC=0.64ppm at pH 7.5 without CYA in the water). This has been chosen as a good compromise between algae killing times and keeping the water swimmable, not damaging the equipment and reasonable amounts of chlorine to be added.
Higher levels would burn off very quickly under UV anyway, and you'd be topping up chlorine constantly to maintain slam level.
- Mar 5, 2020
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I had at the back of my mind that 40% is about 0.32ppm HOCL (or 0.64 ppm FC without CYA)? Isn't that more like Mustard SLAM what you are referring to?
- May 23, 2015
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Could be. I was just typing off the top of my head since I wasn’t near my desktop to do the detailed calculation. Basically it comes down to …. A LOT MORE HOCl than normal. But not so much as to start causing damage or wasting a lot of money on liquid chlorine.
- Mar 5, 2020
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Yeah, that's what I figured. The A LOT MORE is what counts, and were all working from the back of our heads...
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