I had a yellow algae problem. I was advised to add shock and algecide. Now the Chlorine and Bromine (combined in my test kit) are sky high and so is the pH. I can add muriatic acid to adjust the pH down,but with the high Cl and Br when will it be safe for swimmers?
What chemitry levels are safe for swimmers?
- Thread starter mcrisanti
- Start date
- May 3, 2014
- 62,768
- Pool Size
- 6000
- Surface
- Fiberglass
- Chlorine
- Salt Water Generator
- SWG Type
- Pentair Intellichlor IC-40
Pinch a penny 5 way test kit I think it's OBO, 5 drops and phenol red,5 drops for pH. What I don't understand as a retired Chemist is if the pH is right how can the alkalinity be off?
1) the Ph hasn't swung yet, but surely will.
2) 10+ FC invalidates the Ph test so maybe it's not right.
- May 3, 2014
- 62,768
- Pool Size
- 6000
- Surface
- Fiberglass
- Chlorine
- Salt Water Generator
- SWG Type
- Pentair Intellichlor IC-40
pH test is not valid if FC is above 5 (or possibly 3) ppm with that kit.
You need a proper test kit. I suggest the TF-100/Pro or Taylor K2006C. A proper test kit is needed to get the accurate water chemistry results needed to follow the TFP protocols.
Ok, I'll look into that test kit, but it doesn't answer my question. What levels are safe for swimmers?
- May 3, 2014
- 62,768
- Pool Size
- 6000
- Surface
- Fiberglass
- Chlorine
- Salt Water Generator
- SWG Type
- Pentair Intellichlor IC-40
It is safe to swim if your FC level is between minimum and SLAM level based on your CYA. The pH should be in the 7's.
FC/CYA Levels
FC/CYA Levels
The issue is the test kit. The kits has a tube for bromine and chlorine but hopefully you didn’t add any bromine so you can ignore that. The kit isn’t all that accurate if you are interested in detailed alkalinity and pH, then one of the better kits are needed.
I added algecide which is NaBr so yes there is some Br. So, it is better to have the test kit that splits them out. My issue is I have a pool of crystal clear water with high test results and I don't know if it's safe for my wife or grandkids to go in. I don't want anyone's skin/eyes burning or bathing suits fading. So, if I had the proper test kit what would be safe, does anyone know?
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- May 3, 2014
- 62,768
- Pool Size
- 6000
- Surface
- Fiberglass
- Chlorine
- Salt Water Generator
- SWG Type
- Pentair Intellichlor IC-40
Most would advise you to not add any more bromine to the pool water. I don’t have experience with it, but understand it can be very problematic in a pool.
- Mar 5, 2020
- 3,221
- Pool Size
- 66000
- Surface
- Plaster
- Chlorine
- Salt Water Generator
- SWG Type
- Astral Viron V35
There is no kit that can split them out.
Have a read through this article about bromine in pool water:
Sodium Bromide - Further Reading
www.troublefreepool.com
In terms of FC, the FC/CYA ratio is relevant as a proxy for the HOCl concentration which is the relevant sanitizer. With CYA, most of the chlorine will be bound to CYA which doesn't have any sanitizing effects but still shows up as FC in all available FC tests. The TFP recommendations on proper FC levels for the respective CYA levels are summarised here: FC/CYA Levels
FC levels up to the SLAM level for the respective CYA are considered safe for swimming, which is roughly 40% of the CYA. For example, with a CYA of 50ppm, FC up to 20ppm is safe for swimming. The bigger concern is usually to ensure FC being above min for the respective CYA to keep the water algae free and sanitized.
As a retired chemist, you are probably interested in understanding what's behind this. The CYA/FC equilibriums where first described in 1974 by O'Brien:
Richard Falk (alias Chem Geek on TFP) used this together with other publications (that for example show the importance of HOCl rather than FC in the presence of CYA as the relevant sanitizing chlorine species) to further quantify earlier proposed empirical "best guesses" by Ben Powell on required FC levels in relation to CYA using scientific reasoning.
He has summarised his findings in his two sticky threads in The Deep End:
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)...
www.troublefreepool.com
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...
www.troublefreepool.com