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Thread: Something's eating my FC

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    Something's eating my FC

    Hi everyone, I lurked on this board a few years ago when we had a pop-up Intex pool. Your advice helped me keep the water crystal clear.

    Over the winter we purchased a new home with an inground pool and a separate hot tub. (I like to think of it that we purchased a pool and hot tub and a home came along with it).

    Anyways, I opened up the hot tub two weeks ago. I followed the instructions from hillbilly to decontaminate the tub and refilled. I then added some liquid chlorine and also put some 1" tabs in a feeder to also get some CYA in the pool. now that the CYA is up, I'm only using the liquid.

    I have the TF test kit and my numbers are as follows:

    FC - 5
    CC - .5
    CH - 100
    TA - 200
    PH -7.5
    CYA - 30
    Temp - 100

    Water is clear. Before we go in for a soak I'll bring the FC up to 7 and afterwards I'll bring it back up to 5. The problem is that in the morning my FC is back down to .5 or 1. I'll bring it back to 5 and then when I get home from work, same thing, down to 1.

    Is this normal? Since the pool is covered, I wouldn't expect to lose anything to the sun. Does the high temp of a spa somehow reduce FC?

    There's something on the tub that adds ozone. What does that do? Does ozone eat FC?

    Please help a new hot tub owner. Thanks in advance.
    28K, 20' x 40' IG - Vinyl Liner, Hayward DE Filter, 1.5HP Pump, 250K Hayward BTU Heater, Aquabot Breeze 4WD robotic cleaner

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    Re: Something's eating my FC

    Good morning!

    Go back to the basic premise that only two things consume chlorine.....sunlight and organics (algae) in the pool. Your CYA is just a little low so the sun may be consuming SOME of the chlorine but I don't think enough to account for that loss.

    So, the only thing that's left is organics. You need to shock the pool. Follow the directions in Pool School and stay with it until that consumption stops.
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

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    Re: Something's eating my FC

    Ozone purifies water and air very quickly and efficiently, 3,000 times faster than chlorine. It kill bacteria and virus. If you want, you could just try turning off diconnecting your ozonator to see if that makes a difference. Ozone will react with chlorine to produce chloride (salt) and chlorate. So they do destory each other. But anyway unplug ozone shock it and see what you have then. Let us know


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    Re: Something's eating my FC

    But anyway unplug ozone shock it and see what you have then. Let us know
    If you disconnect the ozonator, I would not shock it because then you will not know which action stopped your FC loss.......do one or the other and test FC carefully but not both.
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

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    Re: Something's eating my FC

    Siamese - the hot tub is seperate from the pool? and it's covered during the day (I assume a hard top cover?) so none of the water in the hot tub is transfered to the pool? And the Pool is holding FC fine - just not the spa?

    Honestly if it's just the spa, and if it's not too many gallons - and its entirely seperate from the pool - I would follow the recommendation in pool school and simply refill.
    Helpful links: Pool School; CYA/Chlorine Chart
    24' round AG pool, 52" high, Raypak heater; Waterway 2 spd Pump;
    150 Sq ft. Clearwater Cartridge Filter; Former and DISSATISFIED "Pool Frog" owner
    http://www.PerfectlyClearPoolService.com

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    Re: Re: Something's eating my FC

    Quote Originally Posted by duraleigh
    But anyway unplug ozone shock it and see what you have then. Let us know
    If you disconnect the ozonator, I would not shock it because then you will not know which action stopped your FC loss.......do one or the other and test FC carefully but not both.
    If it holds fc after it is disconnected it would obviously be the ozone being his problem.


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    Re: Something's eating my FC

    If it holds fc after it is disconnected it would obviously be the ozone being his problem.
    I think we're saying the same thing and I don't want to get the thread side-tracked......

    If you do both (shock AND disconnect ozone), either the shock process could stop the chlorine loss (if it is organics) or disconnecting the ozone could stop it (if that's the cause) but I don't see how you would know what the original cause was.
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

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    Something's eating my FC

    Thanks everyone for the speedy feedback.

    Pool mom -- the hot tub and pool are totally separate. The pool's not even open yet, so no mixing of water between the two.

    I had a feeling that the ozone generator may have been involved. I'll try turning that off and seeing if I notice a difference for a few days. If nothing changes, I'll shock it over the weekend. Can I turn that off using the keypad, or do I have to unplug/disconnect something? I'm not sure that the previous owner left the manual.

    If it turns out that the ozone generator is to blame, should I just leave if off for good. Based on the above explanation it sounds like ozone is beneficial, but is a side effect that I have to chlorine twice a day?

    Thanks again.
    28K, 20' x 40' IG - Vinyl Liner, Hayward DE Filter, 1.5HP Pump, 250K Hayward BTU Heater, Aquabot Breeze 4WD robotic cleaner

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    Re: Something's eating my FC

    Duraleigh I see your point. Didn't mean sound rude if I did. Been long long week at work.
    The ozone should be connected to the side of the spa pack. Should be label ozone. As far as if its the problem and should you leave it unplugged.

    I work in a cabin rental and on a daily base I deal with 10 to 30 tubs a day for chemical check/dump cleaning. I half to say from my experience. Tubs with ozones on them the water stays good for longer periods. I don't half to dump them no where near what I do with tubs that don't have ozones. Keeping the filter clean and proper chemical levels the water stays clean for long time for the turn of people that use them. So if it was me I leave it plugged in and try to work a balance out.

    Or like poolmom said dump it and start with fresh water and get everything clean and start over.


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    Re: Something's eating my FC

    A typical ozonator in a residential spa will increase daily chlorine demand (with no bather load) from around 25% per day to 50% per day. You are seeing more than that so your ozonator may be over-powered for your spa and could be using up chlorine too much. As others have noted, turning off the ozonator will tell you if this is the cause.
    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
    12 Fafco solar panels; Purex Triton PowerMax 250 natural gas heater (200,000 BTU/hr output); automatic electric pool safety cover; 4-wheel pressure-side "The Pool Cleaner"

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    Re: Something's eating my FC

    Curious if this ever got worked out. We just picked up a used spa and I am having a similar issue, though mine does NOT have an Ozonator. We keep the spa covered all the time except during use, so no chance the sun is getting rid of the chlorine. I've shocked it a couple times, but seems to no avail. I've got my CYA at around 25 and all other readings are good.
    Chris A.
    20x40 36k gal IG vinyl pool w/diving board & slide | 1.25HP Pentair Challenger motor & pump | 30" Triton TR100 sand filter | Pentair SM-20-3 multiport | Stenner 45MHP2 Peristaltic Pump & 13 gallon carboy (BBB) | Hayward CL200 Tablet Chlorinator (used on pool startup) | TF-100 | 2003 Sundance 850 Altamar hot tub

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    Re: Something's eating my FC

    You might not have adequately decontaminated when you first filled it.

    Shocking is a process, not an event (or product). Crank FC up to 10, check it and refresh it twice a day, until the extreme FC loss stops. I had this sort of thing happen a couple times, usually when I wasn't paying enough attention but relentless shocking cleared it up in a couple days.
    --paulr
    BBB "Intermediate Swimmer"
    IG plaster pool 18.5K gal, Hayward Pro-Grid DE filter, 3/4 HP Hydramax II; Polaris 380, 3/4 HP booster
    AG spa 325 gal, probably Sundance of some kind
    Water testing instructions on one page

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    Re: Something's eating my FC

    Thanks for the feedback. BTW, using BBB method and have tried to keep it at shock level, but seems I can't tend to it often enough to keep it AT shock level for any length of time.
    Chris A.
    20x40 36k gal IG vinyl pool w/diving board & slide | 1.25HP Pentair Challenger motor & pump | 30" Triton TR100 sand filter | Pentair SM-20-3 multiport | Stenner 45MHP2 Peristaltic Pump & 13 gallon carboy (BBB) | Hayward CL200 Tablet Chlorinator (used on pool startup) | TF-100 | 2003 Sundance 850 Altamar hot tub

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    Re: Something's eating my FC

    FC 10 twice a day, morning and night, has been enough for the troubles I've had. If it's not working for you, you might consider a more serious Spa Decontamination.
    --paulr
    BBB "Intermediate Swimmer"
    IG plaster pool 18.5K gal, Hayward Pro-Grid DE filter, 3/4 HP Hydramax II; Polaris 380, 3/4 HP booster
    AG spa 325 gal, probably Sundance of some kind
    Water testing instructions on one page

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    ChiknNutz's Avatar
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    Re: Something's eating my FC

    Yeah, I've been contemplating a full decontamination, but will try a better shock regimen prior to that as I have everything else exactly where I want it. The previous owner gave me all of their old chemicals and after going thru it, discovered they were using something called "Soft Soak" which I guess is another sanitation method based on biguanides. I didn't do anything special when I refilled at my house, so am wondering if I should have gone thru a decontamination due to this. About all I did was clean the reusable filter, put in a new disposable filter (as mine has one of each) and bring up to shock level with dichlor (per the "How to use chlorine in my spa" sticky). Now using straight bleach for chlorine.
    Chris A.
    20x40 36k gal IG vinyl pool w/diving board & slide | 1.25HP Pentair Challenger motor & pump | 30" Triton TR100 sand filter | Pentair SM-20-3 multiport | Stenner 45MHP2 Peristaltic Pump & 13 gallon carboy (BBB) | Hayward CL200 Tablet Chlorinator (used on pool startup) | TF-100 | 2003 Sundance 850 Altamar hot tub

  16. Back To Top    #16

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    Re: Something's eating my FC

    If the previous owner used biguanides, any residue would be eating chlorine; it would be like the tail end of a pool bacqua conversion (there's a whole separate subforum for that). Decontamination is generally the right tactic for the first fill on a previously owned spa, it should take care of any bacqua residue as well. Commonly it's recommended to replace the reusable filter in that situation as well, once your chlorine demand has settled down, because the filter probably has lingering bacquagoo.
    --paulr
    BBB "Intermediate Swimmer"
    IG plaster pool 18.5K gal, Hayward Pro-Grid DE filter, 3/4 HP Hydramax II; Polaris 380, 3/4 HP booster
    AG spa 325 gal, probably Sundance of some kind
    Water testing instructions on one page

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    ChiknNutz's Avatar
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    Re: Something's eating my FC

    Swell. Thanks for the feedback, much appreciated.
    Chris A.
    20x40 36k gal IG vinyl pool w/diving board & slide | 1.25HP Pentair Challenger motor & pump | 30" Triton TR100 sand filter | Pentair SM-20-3 multiport | Stenner 45MHP2 Peristaltic Pump & 13 gallon carboy (BBB) | Hayward CL200 Tablet Chlorinator (used on pool startup) | TF-100 | 2003 Sundance 850 Altamar hot tub

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