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Thread: Have automatic chlorine generator on high, but FC is almost always zero

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    Have automatic chlorine generator on high, but FC is almost always zero

    My Pentair automatic feeder with EZ-Clor big tabs is set on max all the time, and I've shocked my pool about 10 times this summer (I have persistent algae), but still, FC is always zero a couple days after a shock. I know that lots of direct sunlight (which I have) and a high water temp (80-84) increase algae and reduce FC. Perhaps there is too much CYA coming in from the stabilized tabs, and I should reduce my auto feeder to low, and start adding bleach manually?
    IG, vinyl (27 mil), 12,000 G, Apr 2016, OREQ TK400 test kit
    Pentair Tagelus sand filter, Intelliflow variable speed pump, automatic cl/br feeder
    solar bubble pool cover, full sun ~8 hrs/d, water temp 79-84 F May-Oct
    municipal water supply has low nitrates (<0.4 ppm), sulfates, turbidity, TDS
    don't know about phosphates, but suspect they are low (no agriculture around)

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    Re: Have automatic chlorine generator on high, but FC is almost always zero

    This is where we like a full set of test results including your CYA From a trusted test kit

    In your other thread I think you mentioned not having a CYA test. You'll need that along with a FAS-DPD chlorine test kit so you can follow the SLAM process to get rid of algae.

    Pool School - Test Kits Compared
    Pool School - SLAM - Shock Level And Maintain

    - - - Updated - - -

    And I forgot

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    Re: Have automatic chlorine generator on high, but FC is almost always zero

    And I would recommend using the term feeder or dispenser instead of generator, which implies a salt water generator
    My Pool: 18'x36' Grecian. Vinyl Liner, 500# sand filter, SWG.

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    Re: Have automatic chlorine generator on high, but FC is almost always zero

    Thanks folks, and right, I should say "feeder" (which I do in my signature, fortunately). Yes, I know I need to get the full test kit. In the meantime, I suppose I should keep dumping the 1-lb. bags of 73% "super shock" into my skimmer inlet, right? It does clear things up and give me a day or two of non-zero FC. (I still use the pool at zero FC, so long as it's clear, which I suspect you folks recommend against...)
    IG, vinyl (27 mil), 12,000 G, Apr 2016, OREQ TK400 test kit
    Pentair Tagelus sand filter, Intelliflow variable speed pump, automatic cl/br feeder
    solar bubble pool cover, full sun ~8 hrs/d, water temp 79-84 F May-Oct
    municipal water supply has low nitrates (<0.4 ppm), sulfates, turbidity, TDS
    don't know about phosphates, but suspect they are low (no agriculture around)

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    Re: Have automatic chlorine generator on high, but FC is almost always zero

    Quote Originally Posted by szmad View Post
    Thanks folks, and right, I should say "feeder" (which I do in my signature, fortunately). Yes, I know I need to get the full test kit. In the meantime, I suppose I should keep dumping the 1-lb. bags of 73% "super shock" into my skimmer inlet, right? It does clear things up and give me a day or two of non-zero FC. (I still use the pool at zero FC, so long as it's clear, which I suspect you folks recommend against...)
    No!!! No bags of "shock" :

    Those also contain CYA. Please read up in pool school. I posted links above but add this one as well.

    Pool School - ABCs of Pool Water Chemistry
    18*36*23 true "L" vinyl IG 29,000 gallons. SWG. TF-100 test kit.
    http://tftestkits.net/splash-page.html

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    Re: Have automatic chlorine generator on high, but FC is almost always zero

    Thanks a lot AimeeH. I had read the links you sent, but didn't realize I shouldn't use the powdered "shock" because of the stabilizer. I can't follow the full SLAM procedure since I don't have a CYA test, so I'm just going to add about 30 oz of 8% bleach every night until I get the FC level reasonably stabilized at around 1.5 with the CC at zero. I've turned by automatic feeder down to the lowest non-zero setting. Since I don't have a CYA test and want to continue using the pool, I think this is my best bet.
    IG, vinyl (27 mil), 12,000 G, Apr 2016, OREQ TK400 test kit
    Pentair Tagelus sand filter, Intelliflow variable speed pump, automatic cl/br feeder
    solar bubble pool cover, full sun ~8 hrs/d, water temp 79-84 F May-Oct
    municipal water supply has low nitrates (<0.4 ppm), sulfates, turbidity, TDS
    don't know about phosphates, but suspect they are low (no agriculture around)

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    Re: Have automatic chlorine generator on high, but FC is almost always zero

    Without knowing the CYA, you cannot know the required minimum FC level for safe use.

    For example: my pool, with a SWG and CYA of 70, requires a *minimum* FC of 3.2. Without a SWG, that rises to 5.25. Failure to maintain the required min FC is why you keep having algae problems. And if algae can thrive, so can other organic life including pathogens.

    Based on described behavior your pool could have a very high CYA, possibly even requiring a minimum FC in double digits. 10 shocks, at only one bag each, would give you a min CYA of 30-40. Now add in your beginning CYA level, plus feeder use, plus any additional shock bags, and you could easily be looking at 100+ for CYA. And 100+ CYA means 7.5+ FC, minimum.

    It is not uncommon for situations like yours to require a significant water change to start the remediation process. My neighbor ignored my advice and just kept feeding pucks, and ended up with a CYA so high a complete drain and fill was needed.

    You can't fix what you don't understand. Get a test kit.
    My Pool: 18'x36' Grecian. Vinyl Liner, 500# sand filter, SWG.

    My hobbies: Brewing beer and flying rockets.

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    Re: Have automatic chlorine generator on high, but FC is almost always zero

    Thanks AquaRite, I appreciate the advice. I do plan on getting a test kit. in the meantime, I'd rather use the pool after giving it my best shot. I do have some follow-on questions, for you or any other experts.

    -- It sounds like you folks are saying that the EZ-Clor big tabs simply have too much stabilizer, period. This seems a bit odd to me -- wouldn't the makers of tabs know about this issue and choose to put in a minimum amount of stabilizer -- or no stabilizer -- since you can add CYA but not remove it?

    -- Does anyone know whether I can get tabs (pucks) that don't have stabilizer?

    -- Finally (and I understand I may need to go the Chemistry 201 forum for this), I don't understand why the needed FC increases with the CYA, *unless* the measurement of FC includes the chlorine weakly bonded with the CYA. (Otherwise, if the measurement doesn't include chlorine bonded with CYA, then the amount of bleach needed would increase with CYA, but the target FC would not.) Also, do the CYA/FC tables account for the fact that the CYA/cl reaction apparently is reversible, and that cl bonded with CYA still has some disinfecting power?
    IG, vinyl (27 mil), 12,000 G, Apr 2016, OREQ TK400 test kit
    Pentair Tagelus sand filter, Intelliflow variable speed pump, automatic cl/br feeder
    solar bubble pool cover, full sun ~8 hrs/d, water temp 79-84 F May-Oct
    municipal water supply has low nitrates (<0.4 ppm), sulfates, turbidity, TDS
    don't know about phosphates, but suspect they are low (no agriculture around)

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    Re: Have automatic chlorine generator on high, but FC is almost always zero

    Tabs are convenient and this gives them their charm- add chlorine and stabiliser at the same time. The fact is that people blindly keep throwing tabs in without understanding the limitations of high CYA especially when it requires a higher level of FC to maintain adequate levels to keep algae at bay. (Just read a few threads on here). When the pool turns green, they often get caught up throwing shock at the problem to no avail without understanding that their high levels of CYA are at the real problem. Tracking your CYA levels allows you to to avoid this problem but it also gives you the option of using them if you are going away and your CYA allows for it.

    Solid forms of chlorine need a binder of some sort -either calcium or CYA- so no tabs that don't have stabiliser.

    For your final question the best explanation IMO comes from this thread
    11 000 gallons, IG, Fibreglass, Monarch Sand Filter, Davey Typhoon C100M 1HP pump, Davey Chloromatic Mc16CTO ESR SWG, Davey Pool Wall Climba Robot, Daisy Solar Cover,
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    Re: Have automatic chlorine generator on high, but FC is almost always zero

    Quote Originally Posted by szmad View Post
    Thanks folks, and right, I should say "feeder" (which I do in my signature, fortunately). Yes, I know I need to get the full test kit. In the meantime, I suppose I should keep dumping the 1-lb. bags of 73% "super shock" into my skimmer inlet, right? It does clear things up and give me a day or two of non-zero FC. (I still use the pool at zero FC, so long as it's clear, which I suspect you folks recommend against...)
    It seems that you have been using cal-hypo shock? Every 16oz of 73% cal-hypo will raise your CH approx. 5ppm. How much have you used? So, in addition to adding CYA with trichlor pucks, you are also raising CH with cal-hypo.

    With a FC level less than 7% of your CYA not only do you risk algae, but bacteria & virus as well, especially if you fall to zero. You are correct, we will advise you to not swim in that pool.

    As mentioned, please use nothing but liquid chlorine, aka bleach, from this point until we understand your water chemistry better.

    Also, DO NOT add any more chemicals to your skimmer. The localized chemical level & extreme pH wreaks havoc on your equipment over time.

    Slowly pour over a running jet return stream to pull it into the water and help mix. I would add a 1/2 to 3/4 gallon of 8.25% chlorine (laundry bleach) a day as a 'holding pattern'.

    http://www.troublefreepool.com/conte...nate-your-pool

    http://www.troublefreepool.com/conte...efeating-algae

    Once we have a reliable set of test results we can get that pool in great order.

    Dom
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    Re: Have automatic chlorine generator on high, but FC is almost always zero

    - They make non-CYA containing products. Calcium Hypochlorite (cal-hypo) is one, sodium hypochlorite (bleach) is another. TFP method recommends bleach because it is cheap and does not increase calcium hardness. THIS is a non-CYA containing shock product (Calcium Hypochlorite). THIS is a CYA-containing shock product (Tri-chlor). Check the ingredients of any product to determine what you are dumping in your pool.
    Note: I do not recommend these products, I merely pulled the first examples I found for illustration purposes.

    - Look for products that do not contain dichlor, trichlor, or CYA.

    - FC includes bonded Cl, hence the need for FC to equal 7.5% of CYA for non-SWG applications.

    Quote Originally Posted by domct203 View Post
    With a FC level less than 7% of your CYA not only do you risk algae, but bacteria & virus as well, especially if you fall to zero. You are correct, we will advise you to not swim in that pool.
    This. FC = 7.5% of CYA = 0.06% available chlorine. That is why the MINIMUM CYA is 7.5% of CYA. You mentioned you were maintaining a FC level of 1.5ppm. That is unsafe at any level above 20ppm CYA. Since you have been using tri-chlor pucks that adds 3-4ppm per pound, a CYA of 20 or lower is unlikely. And if your shock was di/tri-clor instead of hypo, your CYA level is at least 30-40ppm.

    I normally do not recommend the pool store. But in this case I would recommend a trip today to get your CYA measured so you know what your minimum safe FC is. You can get by on that UNTIL you get your own test kit. Also, pool stores can be a reasonably priced source of liquid chlorine (bleach).
    Last edited by DeadAquaRite; 07-13-2016 at 06:29 AM. Reason: Add info
    My Pool: 18'x36' Grecian. Vinyl Liner, 500# sand filter, SWG.

    My hobbies: Brewing beer and flying rockets.

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    GreatCanadian's Avatar
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    Re: Have automatic chlorine generator on high, but FC is almost always zero

    Quote Originally Posted by szmad View Post
    Thanks folks, and right, I should say "feeder" (which I do in my signature, fortunately). Yes, I know I need to get the full test kit. In the meantime, I suppose I should keep dumping the 1-lb. bags of 73% "super shock" into my skimmer inlet, right? It does clear things up and give me a day or two of non-zero FC. I still use the pool at zero FC, so long as it's clear, which I suspect you folks recommend against...)
    Why would you even think that zero FC is ok? Even if it's clear at zero FC, I guarantee you that it won't be for long. Even at 2 or 3, I'm expecting an algae bloom because of what I am guessing is a CYA level of at least 40. That's a pure guess based on what you say you've added to your pool. Expect trouble. Now if you INSIST on swimming, then get some bleach and bring your FC level up to 7 ppm. That's good for a CYA level up to 80, but is still well below the safe-swim shock value of 16 for a CYA level of 40. I'm not recommending you swim, but if it were me, that's what I would do. I might risk it for myself, but I wouldn't let my children swim in it, simply because I do not know the CYA level, which means I have no clue really as to how much chlorine is necessary or safe.

    GC
    13'x22'x52" 8,000 gallon ProSeries Pool with Borates
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    Re: Have automatic chlorine generator on high, but FC is almost always zero

    Hi All,

    Wow, this is an amazingly knowledgeable group! Thank so much for all the good advice.

    I've done a bit more research and testing, and have come to a number of tentative conclusions, which of course I would like your opinion on. Actual questions are in bold italics.

    #1) I am fairly sure that my CYA level is pretty low -- probably below 20, I'm guessing. Here's why.

    First, I have been using Cal-hypo super shock, which does not have CYA. I got the most recent MSDS for my specific product, and this is what it says: calcium hypochlorite 60-80%, sodium chloride 10-20%, calcium chlorate 0-5%, calcium hydroxide 0-4%, calcium carbonate 0-5%, water 7-16%. So zero CYA there.

    Second, there was no CYA added at initial fill. (I know this because I did the initial fill and chemistry -- only 2.5 months ago -- and my builder turns out to have almost as much knowledge and concern about CYA as the people here!) Third, over the life of the pool (2.5 months) there have been only three big EZ-Clor stabilized tabs in the chlorine dispenser, and these might not even be fully dissolved. (I know because we put in three when we opened the pool May 1 2016, and I have not added anything since. Moreover, I've kept the feeder on "low" for about half the time.) So the only source of CYA in pool is from three (partially) dissolved "pucks". That cannot be a lot.

    I've also determined that my daytime loss of chlorine in full sunlight is very rapid -- it goes from 2-5 to zero really quickly (by the end of the afternoon). This suggests to me relatively little CYA -- if there was a lot of CYA, the nature of the CYA-HOCl equilibrium (way to the CYA side) suggests that the loss of chlorine in sunlight would be slower.

    ​Does anyone know approximately the increase in CYA (say per 1000 gallons) per one EZ-Clor big tab?

    At some point I will measure my CYA, but for now I am confident it is low. To keep it that way, I have turned my dispenser down to almost zero, and will not add anymore pucks (meaning that the maximum CYA in the pool henceforth will be from the full dissolution of three large EZ-Clor tabs, and that's it).
    At this point my plan is to put bleach in the pool each night, to get 2-5 ppm free Cl by morning, let it go to zero in the afternoon, then repeat.

    #2) On the advice of this group, I have switched to liquid bleach. I like it better than the Cal hypo powder because it is easier to administer safely, and you can control the amount you put in each time. Now, most people in this group seem to recommend pouring the bleach in front of the jets, but my builder, who is quite concerned about doing everything to maximize the life of my vinyl liner, says that for a vinyl-lined pool with a sand filter, it probably is better to pour it into the skimmer rather than have it sink quickly to the bottom and tend to bleach the liner. What is your opinion here? Specifically, what components in my system (sand filter, variable speed pump) might be degraded by concentrated chlorine?

    #3) My combined chlorine always is the same as free chlorine, whether both are at zero or 1-5. My test kit says this is good. Do you agree, or should CC be zero?

    #4) Finally, I enter the troubled territory of phosphate removers. I have read the posts here and am persuaded by the TFP experts, with one I hope non-controversial qualification: although the use of phosphate remover doesn't change the recommended FC (vs. CYA) level, it *can* reduce the loss rate of FC, especially under my conditions: full direct sun almost all day and high water temperature, which means that phosphate level almost certainly is the limiting growth factor. These conditions, plus my low CYA, mean that my FC drops to zero pretty rapidly over the afternoon. The use of a phosphate remover to reduce algae will tend to reduce the rate of FC consumption towards algae destruction, thereby leaving a higher afternoon-average FC level for bacteria removal. I understand that there is an extra cost to this, but given my decision to let me FC ride down over the afternoon, the benefit of slightly higher time-averaged FC is worth it to me (I think). But, I respect your opinions, so -- ​Any thoughts on this?
    IG, vinyl (27 mil), 12,000 G, Apr 2016, OREQ TK400 test kit
    Pentair Tagelus sand filter, Intelliflow variable speed pump, automatic cl/br feeder
    solar bubble pool cover, full sun ~8 hrs/d, water temp 79-84 F May-Oct
    municipal water supply has low nitrates (<0.4 ppm), sulfates, turbidity, TDS
    don't know about phosphates, but suspect they are low (no agriculture around)

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    Re: Have automatic chlorine generator on high, but FC is almost always zero

    Forget the phosphates. It's a pool store sales tactic.

    Per chemgeek
    "the net effect is that in 10,000 gallons 1 pound of Trichlor gives 11.0 ppm FC and 6.7 ppm CYA while 1 pound of Dichlor gives 6.6 ppm FC and 6.0 ppm CYA."


    Get your CYA to 30, SLAM, OCLT, raise CYA to 60, maintain FC 5-7, CC <1
    My Pool: 18'x36' Grecian. Vinyl Liner, 500# sand filter, SWG.

    My hobbies: Brewing beer and flying rockets.

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    Re: Have automatic chlorine generator on high, but FC is almost always zero

    On your first question......use pool math. It is linked at the top of the page, put in your pool volume and there is a section at the bottom where you can play with the effects of aging different chemicals.

    The second about CC......how are you testing this? Is it a reagent drop test?

    If your CYA is low, you will lose more chlorine in the pool due to sun. With a new liner and too low CYA, chlorine in high amounts can be more damaging to the liner that with proper CYA/chlorine amounts

    Cal hypo adds calcium which also will build up over time.

    As far as adding bleach/liquid chlorine in front of a return, you should always brush a bit to mix up any chemicals you add and I'd disagree with builder on that one.......unless of course you aren't brushing to mix which I'd never advise.

    Hope I answered those well enough.
    18*36*23 true "L" vinyl IG 29,000 gallons. SWG. TF-100 test kit.
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    Re: Have automatic chlorine generator on high, but FC is almost always zero

    You have to reliably test CYA using a reliable test kit to SLAM. Pool stores are notorious at messing up this test.

    You need the FAS-DPD test to accurately measure chlorine to SLAM.

    There are no short cuts to SLAMming. Add 1/2 a jug of bleach a day until you kit arrives to tide you over. When the kit arrives post up your results and we can help you.

    It won't take long for you save more than the cost of the kit. The cost of the kit is nothing compared to the bags of "shock" you buy.

    TFP is about knowing what your pool needs using accurate, recommended test kit, and only adding what it needs.

    It is up to you to learn to take control of your pool and follow the TFP way.
    Karen
    33K IG w spa plaster, Pentair 1HP Whisperflo, DE Filter, SWG CircuPool RJ-60, Dolphin Triton Plus, Raypak Dig 336K BTU, TF-100.
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    Re: Have automatic chlorine generator on high, but FC is almost always zero

    Quote Originally Posted by szmad
    ....... At this point my plan is to put bleach in the pool each night, to get 2-5 ppm free Cl by morning, let it go to zero in the afternoon, then repeat.......

    More than once it has been advised to not let your FC drop below the minimum level for your CYA to maintain sanitary conditions.

    Why do you want to risk the development of algae or bacteria by letting your FC go to zero daily?

    Dom

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    Re: Have automatic chlorine generator on high, but FC is almost always zero

    Thanks DeadAquaRite, that is helpful. So my three 8-oz tabs of Tricolor have added only 8.4 ppm CYA and 14 ppm FC over 2.5 months.

    Now everything is becoming clearer to me. Given that I've had very high sunlight and algae growth, and now know I have low CYA, it's not surprising that the addition of 0.18 ppm FC per day (from the tri-chlor tabs in the feeder) disappears quickly, leaving me to constantly shock (with Cal-Hypo) to have any semblance of FC for some of the time.

    I understand the reason that most (if not virtually all) experts here recommend against phosphate removers, and am not making a decision based on ignorance about the science. I get that maintaining the FC at the concentration necessary to kill bacteria will also kill algae; my point, as I said above, is that removing algae (by means other than FC) reduces the FC loss rate, which means either a lower rate of FC addition to maintain a constant concentration, or else a higher time-averaged concentration given a constant rate of FC addition. This is true even if the dominant FC loss route in my pool is from UV dissociation.

    I think there is no harm in running a $140 experiment with one container of phosphate remover, which should last a year. The test will be to see whether I reduce the frequency or amount of my bleach input. But first I will need baseline frequency/amount numbers from the bleach protocol, which I have only just started.
    IG, vinyl (27 mil), 12,000 G, Apr 2016, OREQ TK400 test kit
    Pentair Tagelus sand filter, Intelliflow variable speed pump, automatic cl/br feeder
    solar bubble pool cover, full sun ~8 hrs/d, water temp 79-84 F May-Oct
    municipal water supply has low nitrates (<0.4 ppm), sulfates, turbidity, TDS
    don't know about phosphates, but suspect they are low (no agriculture around)

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    Re: Have automatic chlorine generator on high, but FC is almost always zero

    You keep focusing on algae when the real danger is bacteria and viruses. It's certainly not a risk I would take or subject to my family and friends.

    Clear does not mean the water is safe.

    You're getting excellent advice here. I hope you use it.
    20k IG vinyl liner/Aqua Rite SWCG, T-15 cell/Hayward Pro Grid 6020 DE filter/Polaris 280 with booster pump/Hayward Superpump 1 hp/city water/pool installed March 2004

  20. Back To Top    #20

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    Re: Have automatic chlorine generator on high, but FC is almost always zero

    Quote Originally Posted by szmad View Post

    I understand the reason that most (if not virtually all) experts here recommend against phosphate removers, and am not making a decision based on ignorance about the science. I get that maintaining the FC at the concentration necessary to kill bacteria will also kill algae; my point, as I said above, is that removing algae (by means other than FC) reduces the FC loss rate, which means either a lower rate of FC addition to maintain a constant concentration, or else a higher time-averaged concentration given a constant rate of FC addition. This is true even if the dominant FC loss route in my pool is from UV dissociation.

    I think there is no harm in running a $140 experiment with one container of phosphate remover, which should last a year. The test will be to see whether I reduce the frequency or amount of my bleach input. But first I will need baseline frequency/amount numbers from the bleach protocol, which I have only just started.
    You are seriously overthinking this, to the point where your pool is regularly growing algae and may always be unsafe for swimming.

    To summarize the recommendations here:

    1. Add half a gallon of bleach a day until you can get a proper test kit.
    2. Get a proper test kit.
    3. Test your water.
    4. Adjust your CYA to 30.
    5. SLAM
    6. Adjust your CYA to 50-60 after the SLAM
    7. Maintain as per TPF guidelines re: Cl/CYA ratios
    8. Enjoy your crystal-clear pool.
    50,000 gallon plaster in-ground salt pool with two 60 sq ft DE filters, two Intellichlor IC60 SWGs, two Intelliflo VS pumps, two Whisperflo pumps, two Pentair 400K BTU NG heaters, PCC2000 in-floor cleaning system...two everything.

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