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Thread: Please help with puzzling staining problem...

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    adelman's Avatar
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    Please help with puzzling staining problem...

    I need help diagnosing a staining problem in a plaster pool. First, more information about the pool. I hope this isn't too long winded, but I'd rather not have a long series of follow up questions because I left something out. Bear with me...

    It is an approximately 10 year old 20' x 40' below-ground white-plaster gunite pool with an average depth of 5.5' located in Santa Cruz, California at an elevation of 500' (moderate climate). Water is circulated by a 1.5HP pump through a Triton TR-100 filter loaded with 600# of sand. The bottom is swept with a Polaris 280 robot that runs nightly. The pool is heated with a Pentair MiniMax Plus 400 kBTU heater and passive solar panels. It is covered with a mechanical cover that rides on two rails under the coping and retracts into a below-grade vault when open. The pool was originally filled with local well water, and although I do not have historical test data, the water is generally known to have high alkalinity and suspected moderate iron and manganese content (although we do not experience iron staining on our dishes or toilets like some other regions of Santa Cruz do). There are no natural features that would induce water aeration.

    For the past 10 years, the only "water" maintenance that it has received is that which I was taught by the PB. Chlorination has been with trichlor tablets in a floater as necessary to keep the CL between 1 and 3 ppm, which was all that was required to keep the water sparkling clear. If for some reason the water ceased being sparkling clear, 1 gallon of 12% liquid chlorine was added and this would always fix the problem. The pool sees VERY light use, just my wife and I, with one annual summertime party where it sees a single day of heavy use, after which 1 gallon of 12% chlorine was added. Typically it is heated from late March to early September using mostly the solar and occasionally the propane to a temperature of 88F, and it is not "closed" in any freezing sense of the word, but winterized by draining the solar and turning down the propane heat (the heater is programmed to run 10 minutes a day; we find this helps keep spiders and mice out of the burner tubes). It typically spends most of the winter in the mid 50s F. When not in use, the cover is kept closed, so the pool sees very little light. Acid was added as necessary to keep the pH around 7.4, but as the pool aged the pH would hover around 7.2 without the addition of any acid. Backwashing occurred 1-2 times/year even though the pressure never increased enough to notice, nevermind warrant it.

    A few months ago, my wife noted that the pool looked more sparkling green than blue (not an algae type of look to me, crystal clear, but green tinged). I added the obligatory gallon of chlorine, then another, and nothing touched the green. I took a water sample to my local pool store for advise and was told that the green color was probably suspended particles in the pool and that I should change the sand in my filter (given the age) and add some cellulose to improve the filtration. This advise DID fix the color. I was also advised that my alkalinity was "way too high" (I forget the exact number, but probably in excess of 200) and that I should add acid to fix that problem. When I returned with my pH too low, I was sold something to dump in the pool to raise the pH (which also put the alkalinity right back where it was). This caused me to embark on a personal journey of understanding pool chemistry which led me here. I now have the water chemistry under control, but am questioning what I can do about the stains which have slowly accumulated over the past 10 years.

    Test results, test results...

    My first set of tests with the TFT-100 kit showed:

    pH 6.8 (this was after adding the pool supply suggested acid, I doubt it was this way for long)
    FCL 2ppm
    CCL .5
    TA 110 (this was after attempting to lower the TA).
    CH 400
    CYA 110
    Temp 59F

    Resigned that I needed to do something about the high CYA first, I did a 50% drain-and-refill on the pool to lower it to a more manageable value. My intention was to divert future rain water INTO the pool, instead of just pumping it off the cover, to continue to lower the CYA. Given an annual rainfall of 20" and an average pool depth of 66", it would have taken many years to get the CYA under control with just rainwater (also, we're on a private well, so my marginal water cost is very low). Note that this refill was accomplished by water supplied with a different well than the original fill, but they are within a half mile of each other, and I would expect the fill chemistry to be similar.

    After the refill, the water tested:

    pH 7.3
    FCL .5
    CCL .5
    TA 170
    CH 290
    CYA 55
    Temp 59F

    I next embarked on a long affair of lowering the TA by acid/aeration. I aerated initially at a pH of 7.2 using the Polaris hose with the sweeper removed to introduce a splash on the surface of the pool. I eventually lost patience with this and sunk 50' of 1/4" "drilled" drip irrigation line connected to a 5HP oilless shop air compressor, and I used a calibrated electronic pH meter to keep the pH around 7.0 (but never below) through this process.

    My latest tests:

    pH 7.6
    FCL 4.5
    CCL untested, presumed <.5
    TA 90
    CH 290
    CYA 55
    TDL 500
    Temp 59F

    ...and the water is sparkling clear blue.

    Using the Taylor test kits, the Iron and Copper content are currently below the detection threshold. Since this test was done after the 50% water change, this tells me that there was no copper or iron in solution prior to the change and none in the incoming water. I have not added any sequesterents, but do not know if the PB added some during startup. As far as I know no algaecides have ever been used in the pool.

    A few observations -- Obviously I poisoned my pool by using Trichlor until the CYA accumulated beyond reason. I think this is under control now. Also, I would say that the pool HAS NEVER been effectively Chlorine-shocked, since a gallon could only be expected to raise the FCL by 4ppm and only once, recently, did I use two gallons, but by then the CYA was most certainly 110ppm!

    On to the stains, remember the stains...

    The pool plaster in general has a uniform light green to blue green color to it. This discoloration is not objectionable except that it makes the sparkling white of a recent plaster repair stand out. There are also objectionable mottled darker stains, and I'm not quite sure what they are. I've tried parking a Trichlor tablet on them for an hour and it doesn't touch them. I've also tried Vitamin C and it doesn't touch them. My guess, from the color, would be that this was copper staining, but the copper content of the water is below detect. Could this be copper from the heater that has fully precipitated out so that none is left for the water test to see? Any other thoughts?

    I don't find the condition of the pool so objectionable that I'd be willing to do something as drastic as an acid wash to fix it, but if there were a simpler, chemical, or balance, solution, I'm all ears. At this point, I just want a diagnosis. I do have some plaster fragments from an area of chipping plaster that I could perform destructive diagnostic testing on, but am reluctant to send them to someone with a mass spectrometer.

    The following pictures were taken under direct sunlight, but using an underwater camera. Because sometimes colors don't come across the web quite right, I've included a photograph of a Trichlor tablet as a white color reference. Also note the brown staining running down the stairs is likely metal staining caused by the Trichlor floater "parking" over the stairs; THIS staining readily responds to acid removal and isn't what I'm concerned about.

    http://www.adelman.com/_DSC3958.jpg
    http://www.adelman.com/_DSC3960.jpg
    http://www.adelman.com/_DSC3961.jpg
    http://www.adelman.com/_DSC3962.jpg
    http://www.adelman.com/_DSC3963.jpg

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    Re: Please help with puzzling staining problem...

    Very thorough writeup and you have gained a very thorough knowledge of your pool water chemistry....congrats! The water quality looks great.

    My first reaction is the stains are caused by calcium precipitation. Copper stains would be much darker and, as you indicate, they are certainly not the result of iron content.

    Short of an acid wash, calcium scaling is problematic. Take a look at this thread 2nd-times-a-charm-no-drain-acid-wash-t39173.html?hilit=no%20drain%20acid%20wash and see if that might be something you would try.

    I have never personally dealt with calcium scale so others might have better advice but, from reading here on the forum, all your symptoms seem to indicate that's the problem.
    Dave S.
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    Re: Please help with puzzling staining problem...

    While I would simply replaster, especially now that you have a solid understanding of water chemistry, I must tell you that your solarwarrior page was/is fascinating reading - would make for a primetime movie with Harrison Ford as the lead (and Julia Roberts just for kicks..)

    Would you in hind-sight have made anything differently with the solar, or timing of the components, or something else, knowing what you now know ?

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    Re: Please help with puzzling staining problem...

    If the existence of the staining isn't driving you crazy, you can just maintain the pH a little lower (7.2 or so). That will likely (very slowly) remove the scaling. It has worked for me, and for others on the forum.

    The acid bath as suggested by Duraleigh above is a faster and more aggressive treatment. I wouldn't consider replastering solely for scale formation, but since you do have chipping in areas it's worth thinking about over the next couple years.
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    Re: Please help with puzzling staining problem...

    Quote Originally Posted by duraleigh
    My first reaction is the stains are caused by calcium precipitation.
    Is there a diagnostic test that would easily confirm this?

    Quote Originally Posted by duraleigh
    Short of an acid wash, calcium scaling is problematic. Take a look at this thread 2nd-times-a-charm-no-drain-acid-wash-t39173.html?hilit=no%20drain%20acid%20wash and see if that might be something you would try.
    Sounds like the gist of this thread is to drive the pH down to 5-6 for a few days, but I'd need to bypass the heater to do this safely, and throw in a lot of brushing during the process. Because of the way the heater is plumbed, it would be physically difficult to bypass. There is very little room to attack the PVC to add one, I'm not even sure I could fit a pair of unions in the plumbing and slide the heater back to bypass it with a manifold connecting union-to-union. (My heater is also on its last-legs, so I need to consider it's replacement in the coming seasons).

    Quote Originally Posted by Melt In The Sun
    If the existence of the staining isn't driving you crazy, you can just maintain the pH a little lower (7.2 or so). That will likely (very slowly) remove the scaling. It has worked for me, and for others on the forum.
    The problem happened slowly over time, and I just got used to it, so I'm happy with it being fixed slowly over time. What is the lowest pH that such a long exposure to would be safe for the heater? Assuming I can measure it accurately, you think 7.0 would be ok?

    Is the correct brush to be using a stainless steel one (as opposed to the nylon one that I have)?

    The plaster problems are all on the upper step where they are easy to repair, and the rest of the plaster is otherwise in good shape. I know a replaster is in my future, but I'm hoping that I can hold it off for at least a few more years.

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    OT: About my solar pool system

    Quote Originally Posted by susa
    While I would simply replaster, especially now that you have a solid understanding of water chemistry, I must tell you that your solarwarrior page was/is fascinating reading - would make for a primetime movie with Harrison Ford as the lead (and Julia Roberts just for kicks..)

    Would you in hind-sight have made anything differently with the solar, or timing of the components, or something else, knowing what you now know ?
    One of the first things I learned was that I should have installed solar heat on the pool when we built it (it was a retrofit a few years later) If I did the solar on the pool again, I would seriously consider a direct-DC driven pump. With my low utilization of the pool, I've found that running the filter 2-3 hours a day is enough to keep it clean. I need to run the pump much more than that to solar heat it. The problem is my Compool 3800 controller; there is a presumption that the cleaning demands exceed the heating demands, so you program the cleaning runtime and when heat is available, it uses it. On a cloudy day, it isn't energy efficient to run the pump this extra time. Anyone know of a smarter controller that could be retrofit? Ideally, I want to run the pump during the day only if solar heat is available (and only up to a temperature setpoint) and then run it at night (when power is cheaper) IF it didn't run during the day to accomplish any missed filtering. For a bonus, it should know how to use the solar to cool the pool on summer nights if it gets too hot!

    My direct-DC driven idea was to use a separate, smaller, pump to run the water through the panels and drive this with DC power directly off a PV panel which is colocated with the hot water panels. If there is no sun heating the panels, there is no PV to turn the pump. A perfect, efficient, use of a panel. Then I use my existing 1.5HP pump to do the filtering AT NIGHT when power is cheaper.

    Any thoughts on a smarter controller retrofit? I'm not sure what's out there.

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    OT: my solar PV system

    Quote Originally Posted by susa
    While I would simply replaster, especially now that you have a solid understanding of water chemistry, I must tell you that your solarwarrior page was/is fascinating reading - would make for a primetime movie with Harrison Ford as the lead (and Julia Roberts just for kicks..)

    Would you in hind-sight have made anything differently with the solar, or timing of the components, or something else, knowing what you now know ?
    I realize you're probably talking about my photovoltaic system, but I figure'd I'd break this discussion into two posts to keep them shorter. For those of you who haven't seen it, http://www.solarwarrior.com/ .

    There were a number of design decisions forced by the site layout that affected the inverter system, in particular, the decision to put the panels 700ft from the house. This creates a situation where the few volts of drop over the 700ft of 500MCM copper wiring is sometimes problematic and led to a fight with PG&E over the voltage they were providing at the meter. Basically, the inverts disconnect from the grid at 132V, and my grid is very "hot" in my neighborhood (124V, right at their limit). The inverters see the grid voltage PLUS the drop between the house and the inverter shack, and occasionally disconnect when this happens. This was fixed by forcing PG&E to upgrade the wire from the poll to my house; they actually pulled two conductors of 500MCM copper and a 4/0 neutral through a 2" conduit!!!

    The other annoyance was that, at the time, there were no suitable inverters for a system of this size (since there were no systems over 10kW allowed in California). I really have three, nearly identical, 10kW solar systems, each feeding a different area of the house. This partitioning is annoying in a power failure scenario, for example, during
    the recent multi-day outage in California due to the wind storms I wanted to charge an electric car. The car charger draw exceeded 1/3rd of my total production, so that batteries in that inverter slowly drained as I charged it. Halfway through, I moved it to a charger on one of the other inverters and let the batteries on the first recharge. [One solution I've considered is trying to parallel the three DC busses, but there are issues having separate inverters trying to maintain a float voltage and each measuring it slightly differently; they don't balance well, and you can get circulating power where one charges the batteries while the other sells the power back to the grid!]

    Since installation, I've upgraded the charge controllers from the Trace C40s to the Outback controllers that do MPPT tracking (for the non-solar guys here, the Trace controllers operate by running the panels at the same voltage as the batteries, nominally 48V). Since power is VOLTS times AMPS, you'll find that if you draw less AMPS from the panels, the voltage you get them at goes up, and the power can increase. The Outback controllers experimentally find and track this optimal voltage (it changes through the day) and use a DC-to-DC converter to convert, say, 65V at 100A to 48V at 135A, where the old controllers would just produce 48V at 100A.

    If I did this again, I would probably get an inverter system that used high-voltage DC and series'd the panels up to something like 400V, and run the 400V back to the house where I then inverted it. This would be a difficult retrofit now unless I was willing to lose a garage bay to my batteries, as they would need to move into the house. By doing the inverting closer to the meter, I would get around the issues with the grid voltage. I don't try to stay familiar with it, but there is a lot better inverter technology out there and it is constantly improving, so I'm going to keep my current system as long as it operates before upgrading.

    But I digress. These are mostly site-specific issues caused by that 700ft. Since my system has been installed, two of my neighbors also have built smaller systems (but with no batteries). During the last prolonged power failure, they understood why I have batteries, but it does add a significant amount to the initial and ongoing costs of the system.

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    Re: Please help with puzzling staining problem...

    You could look at a variable speed pump like the pentair vf series - vf is variable flow - you set it for how many gallons to filter and then it stops. The basic pentair SunTouch controller can be configured for night time cooling. However all of the systems I looked at required water to be flowing during a potential solar heating period. Kind of makes sense as the temp sensor is at the pad and won't have an accurate reading of the water unless it's flowing. Here again a variable speed pump would help out as you could run it very low speed which is very energy efficient vs your current pump. I'm in CA too so similar high energy costs - I initially second guessed getting the variable speed pump I have instead of a variable flow which would have given me some more options but even the variable speed one that I have has worked out well. To do it again though I would spend the extra money for the vf but I'm a tinkerer...
    15,600 Gallon, 16' x 32' In-Ground Vinyl Pool
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    Re: Please help with puzzling staining problem...

    Quote Originally Posted by carlscan26
    You could look at a variable speed pump like the pentair vf series - vf is variable flow - you set it for how many gallons to filter and then it stops. The basic pentair SunTouch controller can be configured for night time cooling. However all of the systems I looked at required water to be flowing during a potential solar heating period. Kind of makes sense as the temp sensor is at the pad and won't have an accurate reading of the water unless it's flowing. Here again a variable speed pump would help out as you could run it very low speed which is very energy efficient vs your current pump. I'm in CA too so similar high energy costs - I initially second guessed getting the variable speed pump I have instead of a variable flow which would have given me some more options but even the variable speed one that I have has worked out well. To do it again though I would spend the extra money for the vf but I'm a tinkerer...
    What's the purpose of a variable speed pump in a simple pool like mine, i.e., where I don't have a spa or other features that need higher flow. Why variable instead of just smaller? When would each speed be used?

    I suppose a smart controller could periodically turn on the pump for five minutes to sample the temperature.

    Ken

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    Re: Please help with puzzling staining problem...

    Assuming I can measure it accurately, you think 7.0 would be ok?
    Yeah, assuming you have to pass through the heater and you monitor it, 7.0 would be okay.

    If you can bypass the heater and remove any metal ladder, etc. I would drop it to 6.0 although an ordinary pool pH test doesn't go below 6.8.....you would have to use something else.

    Melt in the Sun reports good luck with 7.0....MITS, how long did you keep it there? Was the scaling pretty thick?
    Dave S.
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    Re: Please help with puzzling staining problem...

    Quote Originally Posted by duraleigh
    Assuming I can measure it accurately, you think 7.0 would be ok?
    Yeah, assuming you have to pass through the heater and you monitor it, 7.0 would be okay.

    If you can bypass the heater and remove any metal ladder, etc. I would drop it to 6.0 although an ordinary pool pH test doesn't go below 6.8.....you would have to use something else.

    Melt in the Sun reports good luck with 7.0....MITS, how long did you keep it there? Was the scaling pretty thick?
    I'm going to look again at adding a heater bypass. My concern about cutting too much PVC is making future heater replacement harder (the return lines disappear into the concrete pad). Obviously I need to install some good unions and buy spares of the same type. There is no other metal in the system except for that in the pumps (the impeller bolt), the skimmer pivot and bucket handle, the valve in the built-in autofill, and the bezel around the light. Are we worried about the low pH damaging these things (I could put on my drysuit and pull the light), or are we worried about introducing the metal from these things into the water leading to future staining problems???

    I have a laboratory digital pH meter, so 6.0 would be no problem.

    Just to understand the chemistry of these low pHs; should I just add acid as necessary to maintain it and let the TA slowly be consumed as the CO2 naturally outgasses (pH unstable at the new value), or should I try to aerate and add more acid to consume the TA faster and result in a stable chemistry at the new pH?

    Could the low pH be damaging to my cover? Should I leave the pool open through the process?

    What is the best way to calculate the balance of Baking Soda vs Soda Ash necessary to recover the pH and TA after the process?

    Ken

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    Re: OT: my solar PV system

    >> During the last prolonged power failure, they understood why I have batteries, but it does add a significant amount to the initial and ongoing costs of the system.

    Heh My quick back of the envelope calculations puts the cost of your system somewhere north of 250 k

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    Re: Please help with puzzling staining problem...

    >> Why variable instead of just smaller? When would each speed be used?

    I run the IntelliFlow VF and feed it just around 95 watts of power, it runs 24/7 from Dec to Mar, small pool also...

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    Re: OT: my solar PV system

    Quote Originally Posted by susa
    >> During the last prolonged power failure, they understood why I have batteries, but it does add a significant amount to the initial and ongoing costs of the system.

    Heh My quick back of the envelope calculations puts the cost of your system somewhere north of 250 k
    Not counting legal fees Yes, but it has already produced north of $110K in power!

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    Re: Please help with puzzling staining problem...

    My scaling was not as thick as that, but I kept it down at 7.0-7.2-ish. Richard320 has had success with much thicker scale than mine, and I'm pretty sure he used the same technique as I did.
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    Re: Please help with puzzling staining problem...

    [center:295e1dtg]Does this look familiar?
    [/center:295e1dtg]

    It's Calcium scale. Here's a thread from a little while ago that shows my progress. It's much improved now from just a couple months ago. I'm just waiting for another good rainstorm to dilute the water some more, it seems to melt away faster with lower CH. Currently at 725 CH.

    This has been done using a stainless steel brush and a whole lot of acid. My TA is about 50-60, and I keep pH between 7.2-7.5 so the CSI is always negative.
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    Re: Please help with puzzling staining problem...

    Quote Originally Posted by adelman
    What's the purpose of a variable speed pump in a simple pool like mine, i.e., where I don't have a spa or other features that need higher flow. Why variable instead of just smaller? When would each speed be used?

    I suppose a smart controller could periodically turn on the pump for five minutes to sample the temperature.

    Ken
    Well you're looking at adding solar right? Solar will require a higher speed then filtering. With a typical two speed pump you run filtering on low speed and solar and vacuuming on high. With a VS/VF pump you can tune for optimal efficiency for each mode. As I understand them, a VF pump can be set to stop once a set volume has been pumped - so if it runs faster for 4 hours of the day for heating it will end up shutting off sooner than if it hadn't run faster for those 4 hours. Susa does something similar so he can explain it better.

    Turning the pump on and off for 5 minutes would only allow the solar to run during those 5 minute spurts, at least with the Pentair controllers. I think to do what you're suggesting you will need to a custom controller with a temp sensor in the pool as I haven't seen a commercial controller that provides solar heating without running the pump to begin with. Do a search on the site and there is someone who has made a unique automation system that he is selling; he may be willing to add the capability you desire. Or you could build your own
    15,600 Gallon, 16' x 32' In-Ground Vinyl Pool
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    Re: Please help with puzzling staining problem...

    Quote Originally Posted by carlscan26
    Quote Originally Posted by adelman
    What's the purpose of a variable speed pump in a simple pool like mine, i.e., where I don't have a spa or other features that need higher flow. Why variable instead of just smaller? When would each speed be used?

    I suppose a smart controller could periodically turn on the pump for five minutes to sample the temperature.
    Well you're looking at adding solar right? Solar will require a higher speed then filtering. With a typical two speed pump you run filtering on low speed and solar and vacuuming on high. With a VS/VF pump you can tune for optimal efficiency for each mode. As I understand them, a VF pump can be set to stop once a set volume has been pumped - so if it runs faster for 4 hours of the day for heating it will end up shutting off sooner than if it hadn't run faster for those 4 hours. Susa does something similar so he can explain it better.

    Turning the pump on and off for 5 minutes would only allow the solar to run during those 5 minute spurts, at least with the Pentair controllers. I think to do what you're suggesting you will need to a custom controller with a temp sensor in the pool as I haven't seen a commercial controller that provides solar heating without running the pump to begin with. Do a search on the site and there is someone who has made a unique automation system that he is selling; he may be willing to add the capability you desire. Or you could build your own
    Already have solar on the pool. During most of the year, I can accomplish the filtering during the normal solar heating run, so it would seem that there would be little benefit to a low speed for filtration-only, since I don't need to do more circulation than that required to heat it.

    What I'm thinking of is a controller that would turn on the pump for a few minutes to make a temperature measurement and then turn it back off UNLESS it were beneficial to use the solar. Not quite an in-pool sensor, but it would have most of the benefits.

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    Re: Please help with puzzling staining problem...

    It seems there are multiple, unrelated subjects in this post. Let's try to keep this thread on the subject of calcium scale. If others want to comment about another subject, let's create a new thread but put Adelman's name in the thread title so he can find it easily and then that subject can continue under a new thread.

    I know we always ask folks to keep most info in the same thread for continuity but these topics seem completely unrelated so let's split 'em up. Thanks
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

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