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Thread: Chlorine: Is there such a thing as too much?

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    Chlorine: Is there such a thing as too much?

    I've been fighting algae the past two weeks and realized the last day or two that I haven't been patient enough to let the chemicals work. I got some liquid shock and playing with an online calculator I put enough in to get the chlorine to 30 PPM. I know normal shocking target is 10 PPM, so assuming the liner isn't getting bleached out, am I wasting it? I figured I'd account for it killing algae and some sun loss today before I can test tonight and add more if I need to.
    27' Round Might Sun AG Pool 18000 Gallon Intex Krystal Clear SWG Hayward Pump/Filter on a Timer

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    Re: Chlorine: Is there such a thing as too much?

    Quote Originally Posted by crokett
    I've been fighting algae the past two weeks and realized the last day or two that I haven't been patient enough to let the chemicals work. I got some liquid shock and playing with an online calculator I put enough in to get the chlorine to 30 PPM. I know normal shocking target is 10 PPM, so assuming the liner isn't getting bleached out, am I wasting it? I figured I'd account for it killing algae and some sun loss today before I can test tonight and add more if I need to.
    what's your CYA, if you've been keeping your FC level at what is suggested for shocking depending on your CYA level, 2 weeks should have killed that algae.

    are you vacuuming too?
    14 x 32 x 6 (ave depth) 20K gallons - IG gunite pool. Challenger 1.5 hp pump and cartridge filter.

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    I am vacuuming. Most of last week was spent shocking, vacuuming what I could every other night and using an algaecide. That did absolutely squat, partly because I couldn't hold the chlorine up and partly because I was keeping the cover on which I found out makes the algaecide less effective. The first part of this week I figured I needed to reset since what I was doing wasn't working.

    CYA was increased last night. A sock works great. CYA was another of my screwups (learned on this site) for why I couldn't hold a high level of chlorine. I was told the tablets would add the stablizer that I needed. Last night I vacuumed what I could, added the CYA, got the alkalinity back up and supershocked. I will check levels again tonight. I will vac again if I have time.
    27' Round Might Sun AG Pool 18000 Gallon Intex Krystal Clear SWG Hayward Pump/Filter on a Timer

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    I did the same thing the other week.. shock to around 30+. The pool was blue and crystal clear in about 2 days. Wanted to make sure everything living in the water was dead, without any doubt.

    Wasting chlorine? Technically, sure, if all you needed was maybe 15ppm. But it's not like sodium hypochlorite costs a lot. Worst that can happen is you maybe have to wait an extra day or two to allow the super high FC level to drop.
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    Worst that can happen is you maybe have to wait an extra day or two to allow the super high FC level to drop.
    Well, in your pool that's true. In vinyl lined pools some additional caution is necessary. The possibility of Super High chlorine levels bleacing a liner pool exists........No one know for sure exactly at what level that would occur (KurtV, are ya' workin' on it?) but a degree of caution is in order.

    Most of us vinyl guys start to get nervous in the 25+ range...CYA level has to be factored in there as well.
    Dave S.
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    Most of us vinyl guys start to get nervous in the 25+ range...CYA level has to be factored in there as well.
    Do you mean that the higher the CYA level, the less we need to worry about bleaching?
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    Do you mean that the higher the CYA level, the less we need to worry about bleaching
    ?

    Well, yes and no. Chemgeek, JasonLion, or Waterbear will be along to bail me out (Please, I beg of you ) soon but, in the meantime, let me try a couple of examples from memory. FC of 25 in a pool without CYA is just that...FC of 25 and possibly may fade a liner. FC of 25 in a pool with 40ppm CYA will drastically reduce that potential for fading....making the effective chlorine down in the single digits.

    That's the best I can do for now. I have seen Richard post this more than once so I comfortable repeating it but we'll need one of the folks above to expound.
    Dave S.
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    How effective, and how corrosive, chlorine is depends on the CYA level. A FC level of 20 without any CYA will damage most metals. Meanwhile a FC of 20 with a CYA of 100 is no problem, less than I would recommend to kill off existing algae.

    Take a look at Ben's Best Guess chart, there is a link in my signature. Somewhere around twice the amount in the shock column is where you are likely to start having risk of damaging things. I don't suggest going much above the shock numbers unless you have to, just to be on the safe side.

    Chem Geek created a nice chart of effective chlorine strength at various CYA levels. At a CYA level of 100, a chlorine level of 100 gives you an effective chlorine level below 5. So the effect of CYA can be pretty dramatic.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
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    Quote Originally Posted by duraleigh
    Worst that can happen is you maybe have to wait an extra day or two to allow the super high FC level to drop.
    Well, in your pool that's true. In vinyl lined pools some additional caution is necessary. The possibility of Super High chlorine levels bleacing a liner pool exists........No one know for sure exactly at what level that would occur (KurtV, are ya' workin' on it?) but a degree of caution is in order.

    Most of us vinyl guys start to get nervous in the 25+ range...CYA level has to be factored in there as well.
    chlorine doesn't bleach liners, low ph does.

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    chlorine doesn't bleach liners, low ph does
    .

    Hmmmm, wonder why they call it bleach?
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
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    Roughly speaking, the ratio of Free Chlorine (FC) to Cyanuric Acid (CYA) gives a rough idea of the equivalent amount of FC with no CYA, but this rule only works well up until the FC to CYA ratio is around 1 to 5. Also note that the disinfecting chlorine, hypochlorous acid, level is roughly half the FC level with no CYA at a pH of 7.5. At higher FC levels relative to CYA, the FC tends to overcome the CYA so the disinfecting chlorine level rapidly increases. So this chart shows columns of constant disinfecting chlorine level and shows the FC at each CYA to get that level. A subset of this chart was used to create "Chemgeek's Best Guess Chart" in the Stickies.

    Now though I believe that the reaction rates, and therefore bleaching rate, of chlorine is dependent on the disinfecting chlorine level, note that at shock levels any errors in CYA or chlorine measurements can cause a somewhat large swing in that disinfecting chlorine level. Some people have reported some bleaching of their vinyl pools that appears to be related to where they poured the chlorine, but that may be due more to the temporary high concentration of disinfecting chlorine rather than any higher level throughout the pool. So pouring chlorine slowly, and perhaps even pre-mixing in a bucket of pool water to dilute it first, may make a lot of sense for vinyl pools.

    There are PBs who will swear that vinyl pools are destroyed by bleach, but these may be cases where the chlorine is poured in quickly and settles at the bottom of above-ground pools where there is no floor drain and therefore poor circulation. The same problem happens with Cal-Hypo if not pre-dissolved.

    I think we'll know more shortly when the proposed experiments are done on some vinyl liner pieces at various chlorine levels (at known CYA levels).

    Richard
    16,000 gallon outdoor in-ground 16'x32' plaster pool; Pentair Intelliflo VF pump; Pentair IntelliTouch i9+3s control system; Jandy CL-340 square foot cartridge filter
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    Chem Geek,

    My own practical experience in the 8 weeks I've had my pool says I am switching to liquid chemicals. I already have a few bleached spots on my vinyl liner from where the powdered form of chlorine landed on the bottom when I shocked with it. If the CYA were higher would it have hurt the liner? I have no idea but I am switching to liquids. The 35PPM or so level that the pool has been at the last few days has not done anything to the liner. I used a liquid poured (slowly) directly into the pool but it dispersed much more quickly.
    27' Round Might Sun AG Pool 18000 Gallon Intex Krystal Clear SWG Hayward Pump/Filter on a Timer

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    Higher CYA levels do reduce the effective strength of chlorine. But when trichlor, dichlor, calhypo, or full strength bleach are in direct contact with the liner the local concentrations of bleach are so high that the CYA has minimal effect.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
    Creator of PoolMath and Pool Calculator. Other handy links: Support this site, TF Test Kits, Pool School

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    Quote Originally Posted by poolio
    chlorine doesn't bleach liners, low ph does.
    WRONG! Low pH can cause a liner to become wrinkled and ruined by leaching out the plasticizers but it will not bleach it....high levels of chlorine will bleach a liner. Both chlorine levels AND pH need to be watched in a vinyl pool. OF the two low pH is probably more of a danger to the life of the liner.

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