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Thread: How important is the CSI for Fiberglass pools?

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    How important is the CSI for Fiberglass pools?

    This is the first time I've owned a pool and I am trying to get a handle on all of the info here. If I plug in the recommended numbers for a fiberglass pool into the pool calculator, I get a pretty negative CSI number. After reading more on the forums, I see now that the low water temp will affect the CSI. I see now that I should let the pH rise a little higher to achieve balance.

    I understand how important this measurement can be for plaster, but how will it affect fiberglass in the negative end of the scale?

    I do have waterline tile and brick coping, so I am thinking I need to pay attention to the CSI for that reason as well.

    I have been told by other sources that as long as I maintain a pH between 7.2 and 7.8, and keep the calcium between 150 and 250, the pool shell will be fine.

    I am enjoying learning the info on this site, but until I become more educated, I want to make sure that I don't do anything that will cause damage to my new pool shell or my expensive heat pump.

    My current test readings are:
    FC = 0 (SWG is automatically off due to water temp)
    Temp = 53 deg
    CYA = 35
    CH = 210
    TA = 120
    Salt = 2700 (I havent kept up with this while it's been cold. If the SWG is off I figure why fool with it.)
    pH = 7.6 (I've been keeping the ph lower than I guess I should. I didn't know I should let it run higher during colder months)

    This gives me a CSI of -0.36. So is this ok for my setup?

    By the way, thanks to everyone for all the great info here.

  2. Back To Top    #2
    polyvue's Avatar
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    Re: How important is the CSI for Fiberglass pools?

    Quote Originally Posted by Savannahphil
    This is the first time I've owned a pool and I am trying to get a handle on all of the info here. If I plug in the recommended numbers for a fiberglass pool into the pool calculator, I get a pretty negative CSI number. After reading more on the forums, I see now that the low water temp will affect the CSI. I see now that I should let the pH rise a little higher to achieve balance.

    I understand how important this measurement can be for plaster, but how will it affect fiberglass in the negative end of the scale? I do have waterline tile and brick coping, so I am thinking I need to pay attention to the CSI for that reason as well. I have been told by other sources that as long as I maintain a pH between 7.2 and 7.8, and keep the calcium between 150 and 250, the pool shell will be fine.

    I am enjoying learning the info on this site, but until I become more educated, I want to make sure that I don't do anything that will cause damage to my new pool shell or my expensive heat pump.

    My current test readings are:
    FC = 0 (SWG is automatically off due to water temp)
    Temp = 53 deg
    CYA = 35
    CH = 210
    TA = 120
    Salt = 2700 (I havent kept up with this while it's been cold. If the SWG is off I figure why fool with it.)
    pH = 7.6 (I've been keeping the ph lower than I guess I should. I didn't know I should let it run higher during colder months)

    This gives me a CSI of -0.36. So is this ok for my setup?

    By the way, thanks to everyone for all the great info here.
    Savannah, welcome to the forum

    Grouted waterline tile could be at risk if the saturation index is allowed to remain at that level for a very long time (months?) or is allowed to get a lot lower, but I would think it's fine. As you've noted (and this is something I've just learned recently) allowing pH to rise a bit during winter is an acceptable practice. In your pool, just a .2 or .3 rise in pH would put the SI back in balance so you wouldn't have to worry about the tile anymore. I'm not aware of any impact that a slightly negative CSI would have on fiberglass.

    Pools with surfaces containing calcium also need to have their CSI above -0.6 at all times to prevent pitting. Vinyl, fiberglass, and painted pools can safely have a significantly negative CSI.

    And here's an excerpt from a thread topic I posted last month from a concern that my pool's CSI was negative.
    Quote Originally Posted by chem geek
    As the temperature of water drops, the pH naturally rises due to the chemical equilibriums involved and this tends to keep the saturation index fairly constant (only dropping a little). So you normally should not fight this and should let the pH rise as the water gets colder.
    You can read the entire thread here: CSI calc - out of balance?

    Lastly, would recommend adding some liquid chlorine or regular bleach to your pool water to get the Free Chlorine level up to 2.0 ppm or so. Even in winter pools need the oxidation that is provided by chlorine. (This presumes that you are running your filter/pump daily and don't have the pool covered.)

    Hope that helps.
    14,555 gal in-ground 16'x29' white plaster Pool w/spa (2007); Goldline Aqua Logic AQL-PS-8 control w/Aqua Cell 15 Salt Water Chlorination (SWCG); Hayward TriStar 1HP (1.85 SF) main / 1.5HP (1.60 SF) spa pumps; Hayward Swimclear cart filter C4025, ColorLogic LED lights; Tankless SP-18-4 electric heater; Polaris 280 cleaner.
    __
    View of spiral galaxy in Ursa Major NGC6217 - Hubble Telescope 2009

  3. Back To Top    #3

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    Re: How important is the CSI for Fiberglass pools?

    As for fiberglass, the concern isn't with the fiberglass itself but with the gelcoat that is used and that sometimes contains calcium carbonate. This is further described in this post. The CSI should be closer to zero to protect the calcium carbonate from dissolving, though in your case you also need it for the grout in the waterline tile since that contains calcium carbonate.
    16,000 gallon outdoor in-ground 16'x32' plaster pool; Pentair Intelliflo VF pump; Pentair IntelliTouch i9+3s control system; Jandy CL-340 square foot cartridge filter
    12 Fafco solar panels; Purex Triton PowerMax 250 natural gas heater (200,000 BTU/hr output); automatic electric pool safety cover; 4-wheel pressure-side "The Pool Cleaner"

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    Casey's Avatar
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    Re: How important is the CSI for Fiberglass pools?

    Welcome to TFP!
    I'd bet you my bikini you'll never get TFP water from a pool store!

    24' Sharkline Venture De Filter

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    Re: How important is the CSI for Fiberglass pools?

    This gives me a CSI of -0.36. So is this ok for my setup?
    From Jason's Pool calculator....
    Less than -0.6 is suggestive of problems for plaster, tile, stone, and pebble pools.
    In other words, a CSI that is more negative than .6, which you are not.

    Those of you who have read my posts over the years know what's coming next.........

    I believe an important principle of BBB is simplicity. The average new forum user comes to this site does not understand many of the very basics of pool water chemistry......i.e. the function of chlorine, normal parameters for pH, CH etc. We should take that into account.

    I have successfully maintained my pool (as have thousands of others on this forum) without ever performing a CSI calculation. If you follow the basic guidelines for maintenance and stay within the parameters for pH, TA, FC, CH and CYA that we suggest. You will fall within acceptable results for CSI virtually every time. If there is an exception (that's realistic) I am not aware of it.

    I consider CSI a tool that can be helpful for some VERY fine tuning of your pool water or a calculation to let you know what you really already should know from basic testing.....that one or more of your basic parameters is out of whack and needs correction.
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

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    Re: How important is the CSI for Fiberglass pools?

    Hey...thanks for the speedy responses. I did see the pool calculator's range of -0.6 to .6. I guess what was confusing me is that when I moused over for more info, I needed a value closer to zero for the calculator to give me a "balanced" response.

    Today, I ran my spa jets a little and upped the calcium just a bit. (we've had tons of rain here anyway and I thought I would just stay ahead of it) Ph is now 7.8 and my calcium is at 260...this gives me a CSI of .03.

    duraleigh, I understand what you're saying about the CSI. I'm sure that it would be easy to over analyze and create work for myself.

    At any rate, I really appreciate all the help. I'm really enjoying learning about all this stuff. Right after my pool was installed, I hired a local guy to balance my water and teach me a few things about maintenance. Needless to say, there wasn't much teaching going on, so, I'm really glad I found this site.

    Thanks again.

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    gtm's Avatar
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    Re: How important is the CSI for Fiberglass pools?

    Quote Originally Posted by Savannahphil
    I have been told by other sources that as long as I maintain a pH between 7.2 and 7.8, and keep the calcium between 150 and 250, the pool shell will be fine.
    The only thing that worries me about this thread is that a pH of 7.2 and a CH in that range might be a problem, at least based on my on experience. It may not be a problem in this case, but I worry a bit about other readers getting the wrong idea.

    I have a fiberglass pool of sorts. Mine was a resin and cloth recover over an old marcite pool, not a shell, so maybe much of this is not relevant to most of the fiberglass owners out there.

    After I took over from the Pool Fool (see my earlier posts for that defintion!), I went to a PS here in Florida that I trust, more or less, and the owner advised me to take the CH up to 400 ppm. I questioned her about it (after readling here and elsewhere) and she said that if I didn't the pool shell would get "soft". She asked me if we were getting white stains on our baggies when we brushed up against the wall.

    Honestly, she nailed it. The wall did feel "soft", and we were definitely getting the white stains on the baggies. You could even get a little white dust of some sort by brushing the wall with your hand. This had been happening for several months before I took over, and before I started reading here, but with the pool turning green every three days or so it seemed like a minor worry at the time.

    Afte reading the OP, I went back through my old test data. When I took over the pH was 7.2 (Pool Fool using TriChlor) and the CH was less than 200 (lots of vacuuming dead algae to waste), which had my CSI below the minimum. After reading here I immediately raised the pH to 7.6 and the "softness" and such went away very quickly. CSI at this point was still in the range of -0.4 to -0.5 or so. I did later raise the CH to 350, which is where I maintain it, but I had no problems once the pH increase raised the CSI above -0.6.

    So what's my point?

    I agree with Dave/Duraleigh that it's easy to make things too complicated. Once I started here and got my numbers in order I haven't worried much about my "CSI". I check the pool wall once in awhile to see if it's "soft", but I've had no problems with it in the -0.4 and greater range (i.e., CSI no more negative than -0.4), and keeping the pH in 7.5 to 7.6 range pretty much guarantees that for the temperature range that I experience.

    But for a new person, such as the OP, who might be thinking that a pH of 7.2 and a CH of 200 are in the allowed range for a fiberglass pool, I would just urge a bit of caution. With numbers similar to those my fiberglass shell was heading into the house on my butt!

    Cheers, Gary
    15,000 gal. IG fiberglass pool w/ 1 hp Hayward Max-Flo and 250 lb. Hayward sand filter
    Located in St. Petersburg, Florida, and enclosed in a birdcage

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