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Thread: Levels of Chlorine Shock on a Plaster Pool

  1. #1

    Levels of Chlorine Shock on a Plaster Pool

    My pool guy moans and groans every year when opening my gunite/plaster pool. I see the plaster as being very tight and in great shape with no flaking, bubbles or soft spots at all. On the other hand he swears that the plaster is a haven for mold spores and that he can't just shock the pool with 1 lb of tri chlor per 10,000 gallons.

    He feels that he has to bring the chlorine level up to around 30ppm to be sure he has killed everything. To me it seems like overkill. He's been in the pool business about 10 years and done this pool for about 3.

    The current condition of the pool is medium green, and no where near a swamp. Just experimenting a few weeks ago I put in 4 lbs of di chlor into the 30,000 gallons and I got a milky blue gray color in a few hours, but did not pursue the full opening then. Without testing, I felt I had something in the range of about 5ppm. It even cleaned the pump room floor!

    So the question....... what do other forum members think of going as far as 30 ppm to open this pool or one like it? Have you heard of an approach like it? Are there any upsides? Any Downsides? Initially, I'm pretty sure he will test no other levels, but will balance the chems once he has it clear. Once he gets there, he is great at having crystal clear water! Among the best!

    I know from reading other posts that others do their chems differently, and my guy say he would too, if this was an easy fiberglass pool.

  2. #2
    Administrator JasonLion's Avatar
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    Re: Levels of Chlorine Shock on a Plaster Pool

    It very much depends on the CYA level. The higher the CYA level, the less effective chlorine is and the more of it you need to use. An FC level of 30 with a CYA of zero is drastically too high. An FC level of 30 with a CYA of 300 is too low and will not do very much of anything to algae. This is particularly an issue when using granular dichlor or trichlor to shock the pool. Bothe dichlor and trichlor contain CYA, so even while you are raising the FC level to kill algae you are also raising the CYA level, making the chlorine less effective.

    Plaster surfaces are less effected by chlorine than other surfaces, so you can use higher FC levels in a plaster pool than you can in pools made of other materials.
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  3. #3
    Mod Squad jblizzle's Avatar
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    Re: Levels of Chlorine Shock on a Plaster Pool

    Wow ... where to start ...

    If you want to learn how to care for your own pool, you really should read Pool School (upper right of page).

    The FC shock level is directly dependent on your CYA (stabilizer) level. If you do not know that, there is no way to know how much chlorine to add to shock (which is a PROCESS not a product your just throw in the pool). If your CYA is 100ppm, the show level is FC 39ppm ... so 30ppm may not even be enough.

    Taking care of a fiberglass pool is no different than a plaster pool except your target levels may be a little different.

    I highly recommend you stop just throwing stuff (and $$) into the pool blindly and read Pool School.
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  4. #4
    Mod Squad zea3's Avatar
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    Re: Levels of Chlorine Shock on a Plaster Pool

    Without a complete set of test results we could not tell you how much chlorine you would need. We advocate following the recommendations from the chlorine/CYA chart or the pool calculator to determine the maintenance and shock levels of chlorine for any given pool.
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  5. #5

    Re: Levels of Chlorine Shock on a Plaster Pool

    An "expensive" test kit really is many times cheaper, per year than not having one.

    If you don't have a good test kit you can't possibly know what your FC should be at.

    I probably spent in total last season the same as one visit to the pool store would cost.
    Aaron
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  6. #6

    Re: Levels of Chlorine Shock on a Plaster Pool

    My guy does have a test kit, and as i mentioned originally, he chooses to balance the chems after he gets the pool clear.

    You can agree or disagree with his approach. I am just putting it out there for the purpose of discussion.

    Here is what he said yesterday which may slightly change things, as I was mistaken on the exact chem he uses:

    " I use the cal-hypo for shocking, which doesn’t contain stabilizer so the high levels of FC won’t also create high CYA levels. I no longer test for CYA because its NEVER low in my experience in pools that I service, since its added to the tri-chlor tabs. And if its too high, there’s nothing you can do to reduce it other than removing water and adding fresh, then of course you defeat the purpose of adding the chlorine you have just added."

  7. #7
    Mod Squad jblizzle's Avatar
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    Re: Levels of Chlorine Shock on a Plaster Pool

    Quote Originally Posted by etbrown4
    " I use the cal-hypo for shocking, which doesn’t contain stabilizer so the high levels of FC won’t also create high CYA levels. I no longer test for CYA because its NEVER low in my experience in pools that I service, since its added to the tri-chlor tabs. And if its too high, there’s nothing you can do to reduce it other than removing water and adding fresh, then of course you defeat the purpose of adding the chlorine you have just added."
    I would counter with ... then why use tri-chlor if it is adding CYA which I do not need and will eventually require me to empty my pool to lower the CYA level to a point where the FC is again effective?

    Why use cal-hypo that is adding CH which when high enough will start to result in scaling on the pool surface and again ... require you to empty the pool to lower to correct levels?

    This is the problem with "pool guys" they only come 1 time a week and your pool needs chlorine added everyday ... so they use the tablets which eventually require you to empty the pool why you can not keep it from turning green.

    If this is the process you are happy with and don't mind changing water ... that is your decision.

    We try to explain how to take care of your pool yourself by understanding what is and is not needed and at the same time saving you money.
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  8. #8

    Re: Levels of Chlorine Shock on a Plaster Pool

    Op here.

    Ok so my guy uses cal-hypo to shock the pool. Maybe he got to 20ppm, maybe 30. Don't know.

    24 hours later the pool is now 75% clear.

    Curious that others think of his use of cal-hypo for this purpose. What are the advantages? The disadvantages?

    Is he right that it does not add to the cya?

    One he balances all the chems he comes 2x per week. And he, just like a huge percentage of the pool service guys in the country, uses tabs in the chlorinator.

  9. #9
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    Re: Levels of Chlorine Shock on a Plaster Pool

    Does not add cya, adds ch. someone detailed this in a post above.
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  10. #10
    Mod Squad jblizzle's Avatar
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    Re: Levels of Chlorine Shock on a Plaster Pool

    See my post above ... too much cal-hypo will raise CH which may eventually result in scaling if the pH is not controlled.

    Pucks are relatively cheap and easy which is why the pool guys use them ... what do they care if suddenly there is an algae bloom in your pool and have to make a trip out to "shock it" or suggest you replace water ... you are the one out the use of the pool if/when that happens.

    That is great that he comes twice a week (more than most I would guess).

    If you have no problem replacing water when CYA or CH get too high, then press forward. I am not trying to change your mind just tell you the facts.

    Bottom line: Some of your time/understanding and using bleach can give you a clear pool ... probably for less money than a pool service.
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