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Thread: To Shock or not to Shock?

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    To Shock or not to Shock?

    Hello all. First post, long time viewer.

    First some background... I built this pool 4 years ago, and have managed it myself since. I did the usual Trichlor/Dichlor chlorine feed for the first 3 1/2 years until I found this site. I also was sold on a Paramount Clear O3 when I bought the pool, of which crapped out this year and I haven't replaced it (I'm thinking of doing so, see below). I've been following the BBB for the past 6 months.

    Here's my test results:
    FC .5
    CC .5
    Ph 7.5
    TA 110
    CH 350
    CYA 30

    I've been battling the yellow/brown algae all summer. But, for the most part, my water has been swimmable and very nice all season. However, I seem to be adding much more chlorine this year and wonder if I just have never been able to get rid of what's growing. FYI, I have not done a true shock to the pool all summer. So, here's the question... well, actually a few questions...

    1. Yesterday morning I added (6) 182ml bleach per the pool calculator for a shock. I did an OCLT last night and passed, but my FC levels were (and still are) very low. And, I still have a slight tinge of algae in the corners and in the shady areas. It wasn't very sunny yesterday, but could I have burned all my chlorine off during the day so my reading for FC showed low levels or did I not add enough bleach to get it to shock level? Do I need to keep shocking?

    2. I've been cluing into my CYA, of which I have already done a 75% refill due to numbers well over 120 (during the Phoenix summer no less). When I tested after the refill, I read a CYA of 60. I tested recently, it read 30 (I tested it twice to make sure). My understanding is CYA only goes down by refilling. How long should I wait to verify CYA in another test or is there a chance I tested too soon after the refill?

    3. Speaking of FC, I noted I've always used the ozonator, until it recently failed. I can't help but think my problems this year are in part because I don't have it helping the cause. I've always been able to get by with lower than the recommended FC levels, but I was never able to figure out why. I believe the ozonator shows some benefit. Maybe not so much in the heat of the summer, but during the shoulder seasons. I know this site disagrees with that, but has there been any solid evidence as to their lack of effectiveness?

    4. I have a Taylor K 2005 test kit that appears to be restrictive in its ability to measure FC (the numbers only go up to 5). Is it possible to just rely on the pool calc and the OCLT results, or should I go get a recommended test kit? Right now, I have no idea if my FC levels go above 5!

    Final question... I believe I have some form of algae that is not wanting to go away, and I'm about ready to shock to mustard algae levels just to make sure. Does this sound reasonable? Or, are there any steps I can take to see if I can get by?

    As a side note, along with learning how to truly understand how to manage my pool myself, I've also taken up home brewing over the past few years. I find the chemistry in each area fascinating. Every time I learning something new, I feel I am even more confused. I guess this makes sense since I draw pictures for a living (golf course architect)...

    Thanks in advance!
    27,500 gal in-ground, pebble tec Paddock pool, rectangular shape, 10-ft deep end, 3.5-ft shallow, Jandy cartridge filter, 3hp Pentair variable flow pump, .75hp fixed speed Jandy water feature pump, Haward pool vac, located in Phoenix, AZ

  2. Back To Top    #2
    Richard320's Avatar
    Join Date
    Jan 2010
    San Dimas, CA (LA County)

    Re: To Shock or not to Shock?

    The FAS-DPD test is available separately from You should get one. I can't tell the difference between 4 and 7 using colors - it all looks like 5 to me.

    I'd let the water mix a day after a big drain before retesting CYA. I have no firsthand experience with ozonator. But my pool is crystal clear just the same.

    The 3 criteria for ending the shock are 1) The water is clear - you fail. You still see algae.
    2 and 3 involve precise chlorine testing, which you can't really do with just the color matching.

    Order the FAS-DPD test (you can get refills for your kit, too, and save on shipping) and then do the full shock process as outlined in Pool School.
    16K freeform gunite with spa; Pentair 4000 DE filter; Century Whisperflow 1 HP; Pentair Minimax heater.
    Troublefree does not mean Maintenancefree. It's like brushing your teeth: You can spend a couple minutes a day and pennies a week or go to the dentist once a year and spend several thousand dollars.
    A pool is like a pet - you have to feed it every day, even the days you don't want to play with it!

  3. Back To Top    #3
    Mod Squad jblizzle's Avatar
    Join Date
    May 2010
    Tucson, AZ

    Re: To Shock or not to Shock?

    I don't think anyone disputes that the ozone does something that helps ... especially for indoor pools. But, you still have to maintain chlorine in the bulk water for sanitation. And if you maintain the chlorine in the correct range for your CYA, there is no point to the extra expense of the ozone system. You can simply get by with the chlorine alone.

    Review the mustard algae article in Pool School. I believe you do not raise to mustard algae shock level until you have completed the normal shock process.

    Posted from my Droid with Tapatalk ... sorry if my response is short
    Jason, TFP Moderator
    18k IG pebblesheen pool, Hayward ProLogic P4 w/ T-15 SWG, Pentair 1HP 2-speed Superflo, Hayward 6020 DE filter
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