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Thread: Capacity, more or less

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    Capacity, more or less

    Split off of New above ground owner making chemical system decision. JasonLion

    Quote Originally Posted by waterbear
    Quote Originally Posted by PaulR
    Usually a 52" AG pool has a 4' water depth, which for 12' round works out to 13,600.


    --paulr

    Exactly, but I would just call it 14k gallons and call it a day!
    Remember, it's a pool, not a chemistry experiment!
    Which is exactly the point of the part of my post that you didn't quote...
    --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: New above ground owner making chemical system decision

    Quote Originally Posted by PaulR
    Quote Originally Posted by waterbear
    Quote Originally Posted by PaulR
    Usually a 52" AG pool has a 4' water depth, which for 12' round works out to 13,600.


    --paulr

    Exactly, but I would just call it 14k gallons and call it a day!
    Remember, it's a pool, not a chemistry experiment!
    Which is exactly the point of the part of my post that you didn't quote...
    --paulr
    This part
    Quote Originally Posted by PaulR
    But if your number is letting you get your chems spot-on, that's the number to use. If you keep overshooting or undershooting then you should change your gallons estimate so the chems work out right.
    --paulr
    My point is a difference of 400 gallons is NOT going to show up on testing give the precision of the testkits so why worry about it. 14k is close enough for government work. Many people get trapped into micormanaging their pools and it really is NOT needed!

    Don't know if you are aware but I have a lot of experience with water testing (and not just pools).

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    Re: New above ground owner making chemical system decision

    Quote Originally Posted by waterbear
    My point is a difference of 400 gallons is NOT going to show up on testing give the precision of the testkits so why worry about it. 14k is close enough for government work.
    My point is that you want a number to give the Pool Calculator that gets you answers that work. My own personal experience with my pool is that 18k wasn't quite enough and 18.5k is. Probably because I don't work for the government, I work for me.

    Quote Originally Posted by waterbear
    Don't know if you are aware but I have a lot of experience with water testing (and not just pools).
    I have been hanging around this board long enough to know you have a lot of experience with just about everything!
    --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: New above ground owner making chemical system decision

    Quote Originally Posted by PaulR
    Quote Originally Posted by waterbear
    My point is a difference of 400 gallons is NOT going to show up on testing give the precision of the testkits so why worry about it. 14k is close enough for government work.
    My point is that you want a number to give the Pool Calculator that gets you answers that work. My own personal experience with my pool is that 18k wasn't quite enough and 18.5k is. Probably because I don't work for the government, I work for me.

    Quote Originally Posted by waterbear
    Don't know if you are aware but I have a lot of experience with water testing (and not just pools).
    I have been hanging around this board long enough to know you have a lot of experience with just about everything!
    --paulr
    Yes, I do. And I have a lot of experience with many residentail and commercial pools, not just my own. I also know the precision of the water testing we use (including the computer printouts with the fancy meters that often have a wider varience than a drop test.) While the pool calculator is a useful tool do not lose sight of the fact that it is merely a tool, not the gospal of chemical dosing according to Garp. If you really want to determine the volume of your pool without metering the water that it takes to fill it you can do it with a chemical test.
    http://www.poolhelp.com/ChemicallyDeriv ... olumes.pdf
    Or you can measure the pool by whatever geometrical method would give you an accurate measurment , determine the cubic footage, and multiply that result by 7.48 (the number of US gallons per cubic feet)

    My point is that non of this is really needed! If you are using a certain pool volume and you find it consistanly under or overdoses your pool then by all means move it but when you are first trying to 'set things up' pick a ballpark figures and see how it goes. More ofthen then not you will not need to change it.

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    Re: New above ground owner making chemical system decision

    Quote Originally Posted by waterbear
    My point is that non of this is really needed! If you are using a certain pool volume and you find it consistanly under or overdoses your pool then by all means move it but when you are first trying to 'set things up' pick a ballpark figures and see how it goes. More ofthen then not you will not need to change it.
    Well, we are in violent agreement there; as you may recall I did say "If you keep overshooting or undershooting then you should change your gallons estimate so the chems work out right." I did a quick calculation, got 13,600, and then you started flaming about 14,000, and standing on your vast-experience high horse about it. Why do you care so intensely about something that matters so little?

    tmpfeifer, sorry about the sidetrack, waterbear and I are both being too curmudgeonly tonight.
    --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: New above ground owner making chemical system decision

    ok. so is my gallon figure off then ? We have a 24' AG pool too and I always thought it held 15,200 gal
    Les
    Don't have a pool right now. Just sharing what I have learned over the years!
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    Re: New above ground owner making chemical system decision

    Quote Originally Posted by TizMe
    ok. so is my gallon figure off then ? We have a 24' AG pool too and I always thought it held 15,200 gal
    From my experience a 24" round pool with 4 feet of water in it will dose correctly if you call the gallonage 14K. It's a very common size and I've had many customers with that size pool.
    If you really want to be precise it will be about 13.5k since the formula is pi x (radius)2 x depth to get the cubic feet of water in the pool x 7.48 gallons in a cubic foot of water = 3.14 x 122 x 4 x 7.48 = 13528 gallons
    BUT
    to give you an example of why that small difference in volume is not critical by any stretch of the imagination
    to raise CYA 30 ppm in 14k gallon it takes 3.5 lbs of CYA
    to raise it 30 ppm in 13.5K gallong it takes 3.4 lbs of CYA
    I am using the OnBalance formulas here and doing it manually BTW
    Using the pool calculator gives me 54 oz of CYA for the 13.5k pool (3.4 lbs)
    and 56 oz CYA for the 14k pool (3.5 lbs) so they agree!
    Now tell me that anyone is going to measure out 3 and 4/10 lb of cya! The will round it to three and a half pounds if they weigh it at all!
    Right?

  8. Back To Top    #8

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    Capacity, more or less

    Mathematically computing the capacity of a 24' round 4' deep pool, we find
    pi * 122 * 4 * 7.48 = 13535 gallons.

    I would round this to 13,500 (I have rounded it to 13,600, probably misread the calculator).

    waterbear rounds it to 14,000 and has taken me to task for doing otherwise, on the grounds of the KISS principle, that using a number not rounded to the nearest 1000 is "micromanaging" the pool, and it works well enough.

    I don't dispute that 14,000 works well enough. I do dispute that 13,500 is too complicated for a newbie to understand compared to 14,000, that it makes no difference, and that it is micromanaging.

    Complexity
    If you are doing lots of pool-related calculations manually it is certainly easier to keep track of so-much-per-thousand, and therefore rounding capacity to the nearest thousand makes a lot of sense. waterbear does this a real, real lot, and FOR HIM it makes all kinds of sense to do things that way. When you're testing and dosing loads and loads of pools, it will save all kinds of time and effort to do things that way.

    However, those of us not in the industry are managing ONE pool, not hundreds; generalizing the experience of managing huge numbers of different pools to the management of a single pool is inappropriate in this case. The considerations aren't the same. If you're using the Pool Calculator as we (almost) always recommend, then you're not keeping track of anything except your own pool capacity and it's trivial to enter 13500 instead of 14000. The Pool Calculator even keeps track of it for you, and you only have to enter it once! So there's really nothing to keep track of at all, in this respect. 14,000 is NOT "simpler" than 13,500, IN THIS SITUATION. It is NO different for any individual pool owner, which is probably 90%+ of the people on this board and 100% of the newbies.

    Making a Difference
    I dispute that a difference of 500 gal makes no difference. In this I mainly have my own experience to back it up. It took me a few tries to come up with a capacity that worked for my pool. 18,000 was still undershooting a little; 18,500 works. If it makes no difference then it shouldn't have made a difference; but it did, so it does. YMMV and in this case mine certainly varies from what waterbear said.

    In a 24' round pool, a difference of 500 gallons works out to not quite 2" of depth. In my pool a 2" difference is more variation than the skimmer really likes; hard to imagine that my skimmer is especially unusual in that respect. So the normal capacity variation is going to be less than 500 gallons. With a statistical variation that sufficiently under control it's certainly feasible to find a median capacity number with a granularity of 500 gallons.

    Micromanaging
    Micromanagement here means unnecessarily precise control. In order to be unnecessarily precise it has to be more precise so in this we agree that having a finer granularity of capacity does increase the precision of control. The question then is a value judgement of whether that precision of control is unnecessary.

    In the sense of keeping your pool healthy, precision in most things is not really necessary. Some parameters change very slowly (CH, CYA) some change more or less predictably (TA, pH) and some require constant attention (FC). But those of us who have become comfortable with managing our pools understand that it's all about ranges. In some cases there are rapid consequences for straying one way or the other, and some give and take in the boundaries (supposedly my minimum FC is 3 but I got algae anyway, so now my personal minimum is 4), but mostly not.

    But here we are not concerned with the confident advanced beginner (c.a.b.), but the genuine nervous newbie (n.n.), grasping at whatever straws are easiest to latch onto. Those straws absolutely include the numbers, the chemical parameters that we are constantly being asked about. Anything that contributes to the "fuzz" in what they do to the pool will contribute to the n.n.'s panic, uncertainty, and loss of faith in the TFP recommendations. So, anything we can do to improve the consistency and precision of what we suggest will improve the results seen by the n.n. and therefore their faith in the whole system. THEN they will build confidence in their results, their management of their own pool, and become a c.a.b. themselves.

    The initial estimate of pool capacity is one of those parameters that can often be handled this way. A round AG pool is very tractable that way. A freeform kidney lagoon with spillover spa, not so much; but in the tractable cases it's entirely reasonable to give an estimate that's pretty darn close to the theoretical exact number. Of course in ALL cases we need to qualify that by having the n.n. track what's going on with their own pool and validate the number by experience. But the more often we can give a really good initial guess, the more often we will have happy pool owners.

    And that's really the point, after all.
    --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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    K.I.S.S!

    EDIT: After reading through this a second time I moved this thread to a more appropriate section of the fourm
    Waterbeear, TFP Moderator



    All I am going to say is that there are those that like to make pool care a lot harder than it really it. If you want to see a prime example of what I mean by micormanaging see the above post!
    You have to take into account the precision of the testing methods that we use and where the point of diminishing returns comes in.
    Just because your test result says that you have 100 ppm TA does not mean that you do. It could be 90 ppm or 110ppm. If you are using a smaller sample size that same 100 ppm could now be as low as 75 ppm or 125 ppm. If you are going by the pool store results with their fancy machines it could even be worse than this. Case in point is LaMotte's CYA test with their Waterlink System. This has a precision of +10/-25 ppm so when the printout says you have 48 ppm CYA it could be as high as 58 ppm or as low as 23 ppm!
    Don't know what kind of skimmer you might have but my Hayward skimmer works just fine with the water an inch from the bottom or an inch from the top of the opening so it's about a 4 inch variance. A 2 inch difference in water level in a pool is very common unless you have an autofill and overflow drain and in that case your chemical levels will be changing all the time anyway. Unless, of course, you micromanage by making sure that you always have exactly x inches of water in the pool and if it is off by more than 1 inch you correct it immediately
    While a pool does need to be kept withing certain parameters to be trouble free there is some latitude. Just because a chart says that you must keep your FC at 4 ppm because your CYA is such and such does not mean the world will end if you have 3 ppm or 5 ppm and, with the testing accuracy you very well might. When it says that you need to shock to 16 ppm it does not mean that shocking to 20 ppm is going to be a problem. I have seen a trend develop on this forum for making simple things much more complicated than the need to be.
    I see newbies stress all the time about adding CYA because they are so afraid of overdosing. Just figure out what you need for 40 ppm and put it all in and don't test it for a week. If you misfigured the volume of your pool you will still be in an acceptable range unless you REALLY blew it on the volume. In that case you now know that your first step is to find the actual volume of your pool. However, that is a rarity.

    Just because the pool calculator tells you you need 54 oz of CYA (which work out to 3.4 lbs) are you really going to weigh out 4/10 of a pound or are you going to add 3 and a half lbs. And do you really think that .1 lb of CYA is going to make any real difference in your pool? I bet that a lot of people will just put in 3 lbs or 4 lbs and call it a day. And you know what? They will be fine and so will their pools! Things like the pool calculator are tools, not rules! Personally I prefer the dosing charts from OnBalance since their formula only requires that you have a calculator with you and a table of their constants for the various chemicals. And guess what, the results agree with the pool calculator. I also use BleachCalc a lot. It as some bugs in the borate section but it's a useful program that works. I also use chem geeks spreadsheet. The point is I use all the tools available to me and use them as tools with a bit of common sense! Let's not forget that we are talking about a swimming pool and not a science experiment! The amount of precision that some people try to put into their calculations just ain't there because our test kits don't have that much precision! Once people realize that they will stop sweating the small stuff and enjoy their pool.
    K.I.S.S.

    The test kits we recommend are not ambiguous so it is east to get accurate (repeatable) results. The precision is enough for what we are doing, maintaining a swimming pool but it is by no means anywhere near precise enough to worry about a difference of a few hundred gallons in any pool over about 8-10K gallons. Even in my own less that 7k gal pool and spa it really doesn't make that much difference in my test and dosing results whether i call my pool 7k, 6k or the actual 6850k


    Finally, the term 'advanced beginner' is an oxymoron. You are either a beginner or an advanced pool owner, not both. If there are principles of pool care that you don't know or are not sure about then you are a beginner. If you can stand on your own and know what to do and why without asking for help when things go wrong then you are advanced. If you don't have a clue as to the difference between calcium and chlorine and you use the term "pool thingy" a lot when referring to the equipment you are a newbie.
    Once again, don't make it more complicated that it has to be by creating "CABs" AND "NNs" What is the next step after CAB? Beginning Intermediate Techno Chump?

    Thank you for making my case for me!
    K.I.S.S.

    Now as I see it I can either continue to waste time here debating this with you (not to mention the time already wasted with the PMs) or I could spend my time moderating this forum AND trying to help people with their pools. Ask any of the mods how many man hours (or woman hours) we need to put in to keep things running smoothly around here on a daily basis. We do this because we want to, we don't receive any compensation or anything. And for that matter I believe that I am the only mod that has been modding continuously since the inception of this forum. And you have been a member for what, 6 months now? If I remember correctly you came here with high CYA and were using trichlor. You even asked about using trichlor in your spa. Perhaps in a few years we can continue this once you have 'gotten your feet wet' so to speak.

    K.I.S.S!

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    Re: Capacity, more or less

    What a terrific read on yet another rainy Sunday morning.

    While my brain is slowly being infused with caffeine I'm trying to analyze the perceived discrepancy in balanced water created by 500 gallons. In my mental experiment I'm calculating chemical additions for 13,000, 13,500, and 14,000 gallons and then look at the differences in the amounts. Then I glance at the measuring devices I use, many of which are already pictured in the Pool Equipment Encyclopedia: kitchen measuring cups. Do I really have the capability to add 7.4 oz of acid? No, I don't. I can guess at 7 oz or I can add 8 oz. Do I really even know that the acid is 31.x% as it says on the bottle, or the liquid chlorine is 12.x%? No, I don't.

    Do I really care? No, I don't. It's a pool. By the time the current rain storm has passed, by the time the dogs have been in and out a few times, I have none of those above volumes. Water comes and water goes. A pool is not a static system in a vacuum. It's an ever changing entity; what's true for it today may not apply tomorrow. We cannot treat it like a lab experiment under controlled conditions. It's a hobby and we enjoy it as such. As informed pool owners we have a good grasp on some very basic chemical principles and we apply them reasonably because we understand the limitations of our testing and measuring devices.

    K.I.S.S. all the way.
    — AnnaK —

    12,000 gal AGP, Hayward sand filter, Pentair 2-speed pump, timer.
    Please visit our Pool Issues pages for information about step weights, managing the solar cover, and PoolSkim.

  11. Back To Top    #11
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    Re: Capacity, more or less

    Well said!
    Exactly my point in only two short paragraphs!
    Also, let's not lose sight of the fact that the pool is for swimming in, not testing and ajusting...that's just one of the 'side benefits' if you enjoy that sort of thing (and I think a lot of our members do!)

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    Re: Capacity, more or less

    Fine. 14k works about as well as 13.5k. But they are numbers; neither one is more "complicated" than the other. Nothing anybody has said changes that.

    Pool owners will pick numbers that work for them. As an aside I observe that the OP of the thread that prompted this one is using 13.5k.

    Quote Originally Posted by waterbear
    Finally, the term 'advanced beginner' is an oxymoron.
    If you want to change the subject, start a new topic. I know you think I am humorless but if you ask nicely I will explain the joke. My humor tends to be dry (with or without a twist). It does mean people sometimes miss it.

    The title of this topic is also humorous, by the way.

    Quote Originally Posted by waterbear
    Now as I see it I can either continue to waste time here debating this with you (not to mention the time already wasted with the PMs) or I could spend my time moderating this forum AND trying to help people with their pools.
    Nobody's asking you to debate this with me. Not even me. That's your choice. I posted the long writeup because it seemed that you wanted me to; perhaps I misunderstood. In any case I've conceded the point so continuing it is REALLY a waste of time.

    Yes I am relatively new to this forum, thus the joke in the sig. The point is to learn, right? If you are asserting that I know nothing, that's another new topic. I am doing what I can to contribute, as JasonLion asked. Sometimes I get thank-you notes, too.
    --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: Capacity, more or less

    I have sent you a PM

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