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Thread: Trying to make sure I understand FC/CYA relationship

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    Trying to make sure I understand FC/CYA relationship

    Correct me if I'm wrong or over simplifying it. Just trying to make sure I fully understand FC/CYA relationship. What I know (or think I know) I learned here so I know you guys can clarify and clear up anything I'm still cloudy on....

    FC = Active Chlorine (unbound and available to immediately attack any nasties) + Reserve Chlorine (Chlorine bound to CYA but can still be tapped into, just not immediately).

    If this is a true statement, does anyone know what percentage (assuming there is nothing in the pool at the moment for active chlorine to attack) is active and what percentage is reserve for any given CYA level?
    12300gal IG PebbleTec w/7' raised Spa & Waterfall. Built Aug 2015
    Pentair IntelliFlo VS Pump, Pentair 420 Cartridge Filter, Ultra UV, Auto Fill
    EasyTouch control w/ Remote, Infloor Cleaner w/1.5HP Pump and Leaf Canister
    Stenner 45MPHP10 w/15gal tank, Rainbow 320 Chlorinator, TF-100 Test Kit.

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    Agent99's Avatar
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    Re: Trying to make sure I understand FC/CYA relationship

    Chlorine/CYA Chart.

    This might help you.
    ----Chris----
    25k IG/Spa Figure 8, 18x36, Pebble Sheen Blue Granite, Sta-Rite S8M150 Cartridge Filter, Pentair 460805 400k BTU Heater & 011018 IntelliFlo VarSpd
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    Re: Trying to make sure I understand FC/CYA relationship

    Not really unless you are saying that "minimum FC" would equate to "reserve Chlorine" and the difference between "minimum" and "Target" is the active chlorine. I don't want to make that assumption, but if that is correct, that does help.
    12300gal IG PebbleTec w/7' raised Spa & Waterfall. Built Aug 2015
    Pentair IntelliFlo VS Pump, Pentair 420 Cartridge Filter, Ultra UV, Auto Fill
    EasyTouch control w/ Remote, Infloor Cleaner w/1.5HP Pump and Leaf Canister
    Stenner 45MPHP10 w/15gal tank, Rainbow 320 Chlorinator, TF-100 Test Kit.

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    Re: Trying to make sure I understand FC/CYA relationship

    I'm sure ChemGeek will be along soon.
    Bob - Palm Beach by San Juan Pools. approx 5000 gals., Pentair 320 cartridge filter (all new guts installed by me), Goldline SWG, 'New to me' Kreepy Krauly Sand Shark, Intermec 104 Timer Test kit: TF-100 w/Speed Stir

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    Mod Squad JVTrain's Avatar
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    Re: Trying to make sure I understand FC/CYA relationship

    Until he arrives, here is a great place to look. Using the first chart on the page, you can see the various actual free HOCl versus FC levels at a different CYA levels.
    Pool Water Chemistry

    The equation you can use from that thread as well: (HOCl as ppm Cl2) = (FC as ppm Cl2) / ( 2.7*(ppm CYA) - 4.9*(FC as ppm Cl2) + 5 )
    Joel - TFP Moderator - Minnesota - **Become a TFP Supporter!** Helpful Links: ABCs of Pool Water Chemistry - SLAM Procedure - Chlorine/CYA Chart
    40x20 Pool: 32K Gallons * Vinyl * Bleach Chlorination * Hayward S270T Sand Filter * Pentair SuperFlo 1 HP * Teledyne/Laars Heater * AquaVac Tigershark * TF-100 w/ SpeedStir
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    Re: Trying to make sure I understand FC/CYA relationship

    Here is a link to a recent discussion that does eventually get to this question.

    http://www.troublefreepool.com/threa...l=1#post896220
    Bob - Palm Beach by San Juan Pools. approx 5000 gals., Pentair 320 cartridge filter (all new guts installed by me), Goldline SWG, 'New to me' Kreepy Krauly Sand Shark, Intermec 104 Timer Test kit: TF-100 w/Speed Stir

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    Re: Trying to make sure I understand FC/CYA relationship

    Perfect JVTrain. pabeader. This is exactly what I was looking for.
    12300gal IG PebbleTec w/7' raised Spa & Waterfall. Built Aug 2015
    Pentair IntelliFlo VS Pump, Pentair 420 Cartridge Filter, Ultra UV, Auto Fill
    EasyTouch control w/ Remote, Infloor Cleaner w/1.5HP Pump and Leaf Canister
    Stenner 45MPHP10 w/15gal tank, Rainbow 320 Chlorinator, TF-100 Test Kit.

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    Re: Trying to make sure I understand FC/CYA relationship

    And it answers the follow-up questions I would have had! Don't need to search when you can just ask! lol... (really though, I did search, just wasn't finding the information)
    12300gal IG PebbleTec w/7' raised Spa & Waterfall. Built Aug 2015
    Pentair IntelliFlo VS Pump, Pentair 420 Cartridge Filter, Ultra UV, Auto Fill
    EasyTouch control w/ Remote, Infloor Cleaner w/1.5HP Pump and Leaf Canister
    Stenner 45MPHP10 w/15gal tank, Rainbow 320 Chlorinator, TF-100 Test Kit.

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    Re: Trying to make sure I understand FC/CYA relationship

    OK, now to the question that has been nagging me but I think I have the answer now.

    If I'm planning on trickling in liquid chlorine all day long (when the filter pump is running) using a Stenner pump instead of large doses, wouldn't it be better (less chlorine) to keep CYA at the lower level (around 30ppm for gunite in direct sunlight all day) instead of the upper end of the range (60ppm)?
    12300gal IG PebbleTec w/7' raised Spa & Waterfall. Built Aug 2015
    Pentair IntelliFlo VS Pump, Pentair 420 Cartridge Filter, Ultra UV, Auto Fill
    EasyTouch control w/ Remote, Infloor Cleaner w/1.5HP Pump and Leaf Canister
    Stenner 45MPHP10 w/15gal tank, Rainbow 320 Chlorinator, TF-100 Test Kit.

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    Re: Trying to make sure I understand FC/CYA relationship

    Sure. As long as you don't mind filling your supply tank more often. With the lower CYA you will be loosing to the sun, so have to add more to compensate.
    Bob - Palm Beach by San Juan Pools. approx 5000 gals., Pentair 320 cartridge filter (all new guts installed by me), Goldline SWG, 'New to me' Kreepy Krauly Sand Shark, Intermec 104 Timer Test kit: TF-100 w/Speed Stir

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    Re: Trying to make sure I understand FC/CYA relationship

    Actually I would suggest keeping it at the higher end of the range for the same reason as it is suggested for SWG pools. The higher CYA offers more protection from the sun. One reason a lower CYA is suggested for manually dosed pools is because it is much easier to miss a dose or two and end up needing to SLAM. It also gives a cushion for needing to use trichlor during multi-day trips. Higher CYA is suggested for SWG pools because the automation greatly decreases the possibility of needing to SLAM, so having less chlorine burn off in the sun is of greater benefit. So I would aim for 60 CYA if I were using a stenner pump.
    JD - 28' Round Above Ground Pool, 17,000 Gallons. Dual speed Jacuzzi pump with cartridge filter. Dual speed 1 HP pump, Hayward S210T sand filter
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    Re: Trying to make sure I understand FC/CYA relationship

    I see your point Donldson and that explains why SWG users have a recommended higher CYA level.

    I guess I was thinking if your adding small doses constantly throughout the day and night, you would lose less chlorine to the sun and you could improve on that by the lower CYA/FC and thus less chlorine use overall.
    12300gal IG PebbleTec w/7' raised Spa & Waterfall. Built Aug 2015
    Pentair IntelliFlo VS Pump, Pentair 420 Cartridge Filter, Ultra UV, Auto Fill
    EasyTouch control w/ Remote, Infloor Cleaner w/1.5HP Pump and Leaf Canister
    Stenner 45MPHP10 w/15gal tank, Rainbow 320 Chlorinator, TF-100 Test Kit.

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    Re: Trying to make sure I understand FC/CYA relationship

    You are thinking the same thing I was at one point. What I had to realize is this; Higher CYA does not mean higher FC. It does mean higher base FC but NOT higher FC usage. Daily usage can be similar regardless of CYA level. (too a certain point, and oversimplified like crazy)
    Bob - Palm Beach by San Juan Pools. approx 5000 gals., Pentair 320 cartridge filter (all new guts installed by me), Goldline SWG, 'New to me' Kreepy Krauly Sand Shark, Intermec 104 Timer Test kit: TF-100 w/Speed Stir

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    Re: Trying to make sure I understand FC/CYA relationship

    OK, then is there a way to calculate how much chlorine I will need to add per day to maintain the target level? I see the calculator to determine how much to "reach" a target, but not to maintain it. I guess that might be hard to calculate because of the myriad of factors that goes into it.
    12300gal IG PebbleTec w/7' raised Spa & Waterfall. Built Aug 2015
    Pentair IntelliFlo VS Pump, Pentair 420 Cartridge Filter, Ultra UV, Auto Fill
    EasyTouch control w/ Remote, Infloor Cleaner w/1.5HP Pump and Leaf Canister
    Stenner 45MPHP10 w/15gal tank, Rainbow 320 Chlorinator, TF-100 Test Kit.

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    Re: Trying to make sure I understand FC/CYA relationship

    Is this a correct statement then (albeit very simplified and general)....

    FC day-to-day usage is very similar regardless of the CYA/FC levels, but higher CYA/FC levels provide more protection due to higher reserve levels?
    12300gal IG PebbleTec w/7' raised Spa & Waterfall. Built Aug 2015
    Pentair IntelliFlo VS Pump, Pentair 420 Cartridge Filter, Ultra UV, Auto Fill
    EasyTouch control w/ Remote, Infloor Cleaner w/1.5HP Pump and Leaf Canister
    Stenner 45MPHP10 w/15gal tank, Rainbow 320 Chlorinator, TF-100 Test Kit.

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    Re: Trying to make sure I understand FC/CYA relationship

    That's how I understand it.

    The amount of chlorine needed to keep you at your desired FC is a closely held secret. No not really. It's a game of up and down until you find the sweet spot.

    ChemGeek will probably have a very complex formula for it.
    Bob - Palm Beach by San Juan Pools. approx 5000 gals., Pentair 320 cartridge filter (all new guts installed by me), Goldline SWG, 'New to me' Kreepy Krauly Sand Shark, Intermec 104 Timer Test kit: TF-100 w/Speed Stir

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    Re: Trying to make sure I understand FC/CYA relationship

    Yeah, I'm sure daily usage is noticeably different between sunny and cloudy days and swimmer load, etc. But in order to make sure I order the correct stenner pump, it would be nice to know what the expected daily chlorine need would be, at least in general.
    12300gal IG PebbleTec w/7' raised Spa & Waterfall. Built Aug 2015
    Pentair IntelliFlo VS Pump, Pentair 420 Cartridge Filter, Ultra UV, Auto Fill
    EasyTouch control w/ Remote, Infloor Cleaner w/1.5HP Pump and Leaf Canister
    Stenner 45MPHP10 w/15gal tank, Rainbow 320 Chlorinator, TF-100 Test Kit.

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    Mod Squad JVTrain's Avatar
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    Re: Trying to make sure I understand FC/CYA relationship

    Generally acceptable chlorine losses can vary depending on temperature, sunlight, bather load and other factors but with no bather load, full sunlight summer water temps and adequate CYA levels, somewhere between 2 and 4 ppm FC loss each day could be expected. Some days I lose 1 FC, others I lose 3. Is the pool covered? All these factors will change the FC daily demand. Take the volume of whatever concentration of bleach you're using, necessary to achieve between 1 and up to 6-8 FC and figure out if your pump could do that. In fact, you'd be better off if your pump could achieve that 6-8 ppm FC increase volume in 4 hours of total run time or less to reduce filter pump run time.
    Joel - TFP Moderator - Minnesota - **Become a TFP Supporter!** Helpful Links: ABCs of Pool Water Chemistry - SLAM Procedure - Chlorine/CYA Chart
    40x20 Pool: 32K Gallons * Vinyl * Bleach Chlorination * Hayward S270T Sand Filter * Pentair SuperFlo 1 HP * Teledyne/Laars Heater * AquaVac Tigershark * TF-100 w/ SpeedStir
    Isolated Spa - 345 Gallons

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    Re: Trying to make sure I understand FC/CYA relationship

    Ok, based on that and 3-4ppm loss per day, I can expect to need between 50-70 oz. per day.

    The 45MHP2 can deliver between 1.0 and 15.3 oz. per hour.
    The 45MHP10 can deliver between 2.6 and 53 oz per hour.

    Either should work for just about any scenario of pump runtime/stenner runtime/FC need I can imagine I would need.

    Thanks
    12300gal IG PebbleTec w/7' raised Spa & Waterfall. Built Aug 2015
    Pentair IntelliFlo VS Pump, Pentair 420 Cartridge Filter, Ultra UV, Auto Fill
    EasyTouch control w/ Remote, Infloor Cleaner w/1.5HP Pump and Leaf Canister
    Stenner 45MPHP10 w/15gal tank, Rainbow 320 Chlorinator, TF-100 Test Kit.

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    Re: Trying to make sure I understand FC/CYA relationship

    Quote Originally Posted by TexKSAH View Post
    Ok, based on that and 3-4ppm loss per day, I can expect to need between 50-70 oz. per day.

    The 45MHP2 can deliver between 1.0 and 15.3 oz. per hour.
    The 45MHP10 can deliver between 2.6 and 53 oz per hour.

    Either should work for just about any scenario of pump runtime/stenner runtime/FC need I can imagine I would need.

    Thanks
    I went with the bigger pump so it can deliver it's chlorine in the least amount of operating time (I have mine come on 3 times a day for about 15-20 min per cycle). This should prolong the life of the pump and the tubing.
    20x40 in-ground Bella Blue Pebble Fina pool w/diving board, 1 HP Hayward Superpump, Raypak RP2100 335k BTU NG mV heater, Pentair Quad DE 60 filter, Pentair 261173 multi-port valve, Stenner 45MPHP10 pump w/15 gal tank, Intermatic ET1125CR dual electronic timer, 1.5" lines, two skimmers w/socks, Poolskim, vacuum line, ColorQ Pro 7 kit, TF-100 kit, speedstir, 2 froglogs, Dolphin Discovery Robot. Wine is the answer, what was the question?

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