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Thread: Can't hold chlorine, nitrates

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    Can't hold chlorine, nitrates

    Hi folks, first full year at the new home with a pool. We opened the pool in late may with no problems, balanced it fairly quickly and we were in balance for a while. I have a chlorine tab in each of my two skimmers. The pool sit in the sun the entire day, and temp has been 85-90 for over a week now. And now that the warm weather has it, it seems we cannot hold our chlorine levels. I also noticed in the past few days a red slime (bacteria?) starting to show up in the corners. So I put in 2 lbs of 'super-shock' Thurs evening.

    We had our water tested at a chain pool store yesterday then today again. 0 FC/0TC yesterday. I then added what they suggested of 4 more lbs of the super-shock. I went back today and only .5FC/.5TC remain. They then tested for nitrates, and result was 10. They said I must drain my pool 1 foot, and then add 25lbs of granular chlorine because of the high level of nitrates. I lost confidence in them when she said "nitrates are a mystery". is that really the solution? and what can I do about the red 'slime' ?

    here are my numbers....

    FC= .5
    TC= .5
    PH= 7.6
    TA=50
    CH= 150
    CYA=40

    thanks!
    30k gallon in-ground vinyl, sand filter

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    JasonLion's Avatar
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    Re: Can't hold chlorine, nitrates

    Welcome to TFP!

    Nitrates have nothing to do with it. There are a couple of possibilities, but by far the most likely is that you simply have to shock the pool.[shock:zrpt1tg3][/shock:zrpt1tg3]

    I would avoid using granular chlorine for shocking. The most common granular chlorine is dichlor, 25 lbs of which would raise your CYA level far to much. It could also be cal-hypo, which isn't nearly as bad but will slowly raise your CH level. You have some room to raise CH, so that is alright for a time, but avoid dichlor.
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    Re: Can't hold chlorine, nitrates

    Jason, thanks. I will find some cal-hypo. what about liquid chlorine? i used 4 gallons of 12% when i opened the pool this year.
    30k gallon in-ground vinyl, sand filter

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    Re: Can't hold chlorine, nitrates

    By far, liquid chlorine is the best.
    Dave S.
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    Re: Can't hold chlorine, nitrates

    Here is my update.. since my post on sunday, i added 2 lbs of cal-hypo that evening, and still couldnt hold the levels overnight -- i am using the HTH test kit. So last night i added 4gal of 12% liquid chlorine, and it held to this morning, and the test kit shows still the same bright yellow this afternoon. Will continue to test again tonight and tomorrow morning. I am hoping its taken care of. I've also ordered a k2006 test kit so i can get more accurate results. I'll reply back in a couple days when the kit arrives with my updated numbers.. thanks for your replies!
    30k gallon in-ground vinyl, sand filter

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    Richard320's Avatar
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    Re: Can't hold chlorine, nitrates

    While you're waiting for your test kit, start reading
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    Re: Can't hold chlorine, nitrates

    OK.. so i just ran my first test with the K2006, and here are my results. its been raining here for the past few days, so that's my guess why the PH has dropped. the pool was always clear, but it seems to be more crystal clear now, not as dull. what do you guys think? thanks!

    FC= 3.4
    CC= .6
    PH= 7.4
    TA=80
    CH= 200
    CYA=40
    30k gallon in-ground vinyl, sand filter

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    Richard320's Avatar
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    Re: Can't hold chlorine, nitrates

    Quote Originally Posted by nickyc01
    OK.. so i just ran my first test with the K2006, and here are my results. its been raining here for the past few days, so that's my guess why the PH has dropped. the pool was always clear, but it seems to be more crystal clear now, not as dull. what do you guys think? thanks!

    FC= 3.4
    CC= .6
    PH= 7.4
    TA=80
    CH= 200
    CYA=40
    Raise it up to shock level - that will be 16 for you - to kill off that last bit of Combined Chlorine, then never, ever, let FC drop below 3. But do that before bed. Go swimming now. That's what I think.
    16K freeform gunite with spa; Pentair 4000 DE filter; Century Whisperflow 1 HP; Pentair Minimax heater.
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    Butterfly's Avatar
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    Re: Can't hold chlorine, nitrates

    Now that you have a good test kit, you can see if you pass the three criteria that determine if you are done shocking.
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    Re: Can't hold chlorine, nitrates

    just got home, and ran the full panel of tests. Here are the results.

    FC 3.2
    CC 0.4
    PH 7.4
    TA 70
    CH 170
    CYA 40

    I checked my FC this morning, and it held from last night's FC test. It looks like I just need to keep stable above 3. I'm guessing that I can just use the pool calculator and add either the cal hypo that i have or the liquid. I'm going to add some tonight, and I am going to try to stay above 4 just in case.....

    thanks again for all your help!
    30k gallon in-ground vinyl, sand filter

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    Mod Squad jblizzle's Avatar
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    Re: Can't hold chlorine, nitrates

    Cal-hypo is fine for now ... keep an eye that you do not let the CH get too high.

    You are flirting with the minimum FC level, so shooting a little higher is a good idea.

    Also, save yourself some reagent and use a 10ml sample for your FC and CC test. Each drop will be 0.5ppm instead of 0.2ppm. No need to be that accurate.
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    Re: Can't hold chlorine, nitrates

    yeah, thanks... i wanted to run it on the 25ml one more time to make sure I wasn't too low - still paranoid
    30k gallon in-ground vinyl, sand filter

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    Re: Can't hold chlorine, nitrates

    Any pool, any given day that has sun or bathers means you'll lose roughly 50% of your chlorine.

    Now, if you look at keeping FC at 4ppm, and lose 50% you're automatically 1ppm below minimum. 3ppm is your absolute minimum, never to fall below. When you check the calculator, it shows a range. The high is not a warning of "too high" or a limit, but rather a reasonable high to target for daily FC loss.

    So, for 40ppm CYA your range is 3-7ppm FC. If you start the day with 7ppm, and lose half... you should be no lower than 3.5ppm at the end of the day. Make sense?

    The easiest way to dose your pool is to test after everyone has stopped swimming at the end of the day, and the sun is off the pool. Then add enough to get to the high target for your CYA (7ppm for you), and relax. Unless you have significantly higher loss per day than 50% this works 100% of the time, and after a while you won't even need to test because you'll know what conditions cause certain losses.

    On double cloudy days around here, I don't need to add chlorine till the second night when it falls closer to minimum. Normal usage with sun, I add 3-4ppm (I like to tip the pool a half a ppm now and again) after dark and all is well.

    I love that the pool store said nitrates are a mystery. That's funny. Ask any aquarium/fish keeper... nitrates are not a mystery. I have nitrate test kit for my aquarium... I should go test my pool, just for fun.
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    Re: Can't hold chlorine, nitrates

    Frogabog, since you're an aquarium lover, isn't red slime cyanobacter? Wouldn't you want to shock instead of maintain normal chlorine levels? Or am I all wet here? Yesterday, I noticed it in my birdbath and was quite surprised, but a nearby inland lake had a big fish kill during the heatwave, so I was assuming the conditions included cyano and it carried in with the rain. Hopefully not from my well water!
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