How high can Free chlorine be in SWG

[JazzMan2010]

Hello, after a some help from this board i cleared up several issues with my pool. The largest being almost no FC. After superchlorinating the pool i'm now able to run my SWG by itself. My readings today were
FC 7
CC0
PH 7.2
Alkalinity 110
CYA 70

My question is how high can i have the FC to be safe?

[chem geek]

Your FC level is fine. Ben's Best Guess CYA chart (http://www.poolforum.com/pf2/showthread.php?t=365) gives a maximum FC for your CYA of 10 ppm so you're fine up to that level. You can go higher for shocking when necessary, to 20 ppm in Ben's chart.

Technically, having an FC of 7 ppm with 70 ppm has the same amount of active chlorine (hypochlorous acid) as around 0.1 ppm FC with no CYA so it's a much lower amount than found in most indoor pools since they usually do not have CYA and it's far lower than found in chlorinated tap water. The FC level itself is a measure of chlorine capacity or reserve so is mostly relevant if you were to drink the pool water, which you generally do not do (at least not in large quantities).

Richard

[JazzMan2010]

Thanks for the reply. I did not know that. I'm learning something new everyday here.

[CarlD]

... The FC level itself is a measure of chlorine capacity or reserve so is mostly relevant if you were to drink the pool water, which you generally do not do (at least not in large quantities).



Unless you are my 5-year old!

Seriously, the only other factor you should consider is if you have a vinyl pool there is a chlorine level, depending on your CYA level, that fades the vinyl.

[chem geek]

Seriously, the only other factor you should consider is if you have a vinyl pool there is a chlorine level, depending on your CYA level, that fades the vinyl.
Even this might be somewhat of a myth, or at least not true in practice. Though there is no question that low pH is very damaging to vinyl and that very high levels of concentrated active chlorine can fade vinyl (such as from Cal-Hypo sitting on the bottom of a vinyl pool; Trichlor pucks being much worse due to acidity), even shock levels of chlorine may not do so very quickly. Most fading of vinyl comes from exposure to the UV in sunlight.

A pool owner on another forum put a piece of extra vinyl from their pool in a jar with bleach at high concentration and it did not fade the vinyl over a week compared to another piece not exposed to the bleach. Note that the high pH of bleach prevents the effective FC from getting too high -- the highest equivalent FC possible (i.e. with the same active chlorine level at 7.5 pH) with typically buffered tap water (50 ppm TA) and adding 6% bleach (and not lowering the pH) is around 34 ppm FC (assuming the pH gets to 9.8 from adding the bleach) at a dilution of around 13:1. Pure bleach is ironically even weaker in hypochlorous acid since the pH is high at 11.9 so the 61,700 ppm FC is equivalent to 3.3 ppm FC at a pH of 7.5. Of course, at this high concentraiton the hypochlorite ion starts to become important since even at 1/100th the reactivity, it would be very significant.

People have been shocking in their vinyl pools for years now with no apparent ill effects. Of course, they have been responsible in doing so by pouring slowly over a return flow with the pump running and usually lightly brush the side and bottom of their pool to ensure thorough mixing.

The only reports of problems have been from a few pool service guys or PBs that swear that using bleach in vinyl pools is bad and causes the vinyl to become paper thin and that they've asked people what they've used in their pools when they come out to replace the liner and the person says they were using bleach. However, these people may have been dumping bleach in one place without circulation in which case it would settle towards the bottom of the pool since it is denser than water if not mixed. I haven't seen any such reports from any actual pool user on any pool forum or even in the past couple of years from pool service people or PBs so I don't know exactly what these early reports (5-7 years ago) from service guys or PBs were really about.

Richard