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Thread: Holding FC better than I expected

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    mikemass's Avatar
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    Holding FC better than I expected

    This may be long but want to give all pertinent info, so try to bare with me:

    After opening my pool this season, I quickly discovered that my Salt cell has ran it's life expectancy. BUT before I knew it was bad, the salt was reading too low according to the automated board for the SWG to work (which I expected as I drop about 8" of the water for the winter and then refill for the spring). So I added 5 bags (200lbs) of salt. The board was reading only 2600 after. Still too low for the system to work. I thought: "Wow. I must have dropped more water than I thought prior to closing". So I added another 5 bags which would be the correct calculation to go from 2600 - 3200. At this point my cell was reading only 2800. High enough for it to kick on and actually produce chlorine. But clearly inaccurate according to hand calculations. At this point I manually tested the salt. One test showed 4500, another 4000. Based on what I typically know I need to add and what I actually did, I think the 4500 is more accurate.

    So I brought the cell to Leslies and had it checked out - It failed. I ordered a new cell, which should be here Tomorrow..... In the meantime I had some water adjusting to do. Because when the new cell gets here and hopefully reads proper, it will not work if it is reading too high of salt. So I dumped water. LOTS of it. Luckily I had yet to bring my Calcium and CYA back to proper levels. If I did I would have just dumped them in the woods too. So out with about 10" of high salt water and in with new fresh water. Obviously, the bad SWG was producing no Cl at this time, so I dumped a gallon of 8.3% bleach into pool while filling back up on Sunday. (if you are still with me, thanks)

    Monday early afternoon: Pool high enough to get the skimmers going, so I started the CYA in sock routine. But only added 1/3 of what I needed to get to required amount. I also dumped a gallon of bleach in for good measure.

    Monday night: Pool now full, I checked FC levels - it was 5.0. Sounds about right as Monday was somewhat cloudy. But I really didn't have much CYA dissolved either at this point. Added another 1/3 of my CYA to socks and let pump run. no more bleach.

    Now for the bizarre part:
    Tues night: First I checked my CYA socks. Contents were fully dissolved. GREAT - I'm getting there. Next I checked FC again. 5.0. Sucker was still holding after another day of full sun, no more bleach, and only about 2/3 the CYA added. At this point I added the remainder CYA to the socks but no more bleach.

    Wed night (Last night) I checked the socks. CYA was fully dissolved. So I figure time to test it. Now I hate this CYA test. I feel it is extremely inaccurate and totally subjective as to when that lousy dot actually disappears. It was dusk unfortunately, so not the best of conditions to test in. I tried under a few different lights and can conclude it is definitely greater than 50 but less than 80. (I want to target 70). Anyway, close enough for now till I can try again in the sun.

    Other results from last night:
    pH = 7.2
    TA = 70
    FC = 5.0 (maybe a tad less, but certainly not 3.0) Call it 4.0. Either way I cannot believe how well this pool has held CL for over 2 days (55 hours) of no bleach dosing, of which the first day had virtually no CYA to speak of yet.

    What's your guys' take on all of this?
    25 + year pool owner. Current pool (going on 11th year) - 38K gallon in ground Gunite/White Plaster, Spillover Spa, Hayward Cartridge Filter, Hayward 450k BTU NG Heater, Hayward Goldline Aqua Logic control with T-Cell-15 Salt Water Cell, Dolphin Explorer.
    You Need: Bleach, a A Test Kit & a Bookmark to "Pool School". Now what's your question?

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    Re: Holding FC better than I expected

    How are you measuring FC?
    Built in 1957 44,000 gallon in-ground, Wet Edge Primera Stone in Sky Blue, Intelliflo VF Pump, 600 lb. Pentair Triton II TR-100 Sand Filter, CircuPool RG 60 Plus SWG, TF-100 test kit
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    mikemass's Avatar
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    Re: Holding FC better than I expected

    Five drops of R-0001, followed by 5 drops of R-0002. Cap, shake, hold up to a white cloud, compare color.
    25 + year pool owner. Current pool (going on 11th year) - 38K gallon in ground Gunite/White Plaster, Spillover Spa, Hayward Cartridge Filter, Hayward 450k BTU NG Heater, Hayward Goldline Aqua Logic control with T-Cell-15 Salt Water Cell, Dolphin Explorer.
    You Need: Bleach, a A Test Kit & a Bookmark to "Pool School". Now what's your question?

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    Mod Squad pooldv's Avatar
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    Re: Holding FC better than I expected

    That is weird. Is there a cover on the pool? Maybe add a couple ppm and check again.

    Do you have an FAS/DPD chlorine test to double check? That is the best one. But, the DPD test you have is fine too.
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    mikemass's Avatar
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    Re: Holding FC better than I expected

    no cover and no FAS/DPD. This is what I have always used. Never felt the need to upgrade as I have never had the more common problem of not being able to hold Cl. The only reason I am so on top of this right now if because of the bad salt cell. When my cell is working I don't go crazy testing every night like this. I guess if there's a "problem" to be had, this is a good one.
    25 + year pool owner. Current pool (going on 11th year) - 38K gallon in ground Gunite/White Plaster, Spillover Spa, Hayward Cartridge Filter, Hayward 450k BTU NG Heater, Hayward Goldline Aqua Logic control with T-Cell-15 Salt Water Cell, Dolphin Explorer.
    You Need: Bleach, a A Test Kit & a Bookmark to "Pool School". Now what's your question?

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    Re: Holding FC better than I expected

    I'm pretty sure the highest FC result using the drop test is 5, so you might have had more than 5 and it drifted down and you are still at 5. Best to order the FAS/DPD powder test so that you have a better, more accurate result. It is easy to overshoot your FC is you have really fresh bleach which can be stronger than the amount listed on the label or if overestimate your pool size.

    You can order one from here: TFTestkits.net

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    Re: Holding FC better than I expected

    Quote Originally Posted by kcindc View Post
    I'm pretty sure the highest FC result using the drop test is 5, so you might have had more than 5 and it drifted down and you are still at 5. Best to order the FAS/DPD powder test so that you have a better, more accurate result. It is easy to overshoot your FC is you have really fresh bleach which can be stronger than the amount listed on the label or if overestimate your pool size.
    Yep, that's where I was headed. You were well over 5.
    Built in 1957 44,000 gallon in-ground, Wet Edge Primera Stone in Sky Blue, Intelliflo VF Pump, 600 lb. Pentair Triton II TR-100 Sand Filter, CircuPool RG 60 Plus SWG, TF-100 test kit
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    mikemass's Avatar
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    Re: Holding FC better than I expected

    I had a feeling that might have been it. So on my kit the red at 5.0 is the same as say the red at 8.0, or 25.0 even? Said another way, no matter how high my FC gets, the red won't get any darker than the highest mark on the vial?

    Is this correct?
    25 + year pool owner. Current pool (going on 11th year) - 38K gallon in ground Gunite/White Plaster, Spillover Spa, Hayward Cartridge Filter, Hayward 450k BTU NG Heater, Hayward Goldline Aqua Logic control with T-Cell-15 Salt Water Cell, Dolphin Explorer.
    You Need: Bleach, a A Test Kit & a Bookmark to "Pool School". Now what's your question?

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    Re: Holding FC better than I expected

    That's correct. That is why we use the FAS-DPD. You can't measure over 5 with what you have.
    Built in 1957 44,000 gallon in-ground, Wet Edge Primera Stone in Sky Blue, Intelliflo VF Pump, 600 lb. Pentair Triton II TR-100 Sand Filter, CircuPool RG 60 Plus SWG, TF-100 test kit
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    Re: Holding FC better than I expected

    Out of curiosity can you fill tube on DPD test half pool water and half distilled, do the drops and then double the reading? Example: True FC is 8. Will half and half give a reading of FC 4 and then you double it to have true FC 8?
    23000 gal. IG colored plaster 18x38 rectangular pool with jacuzzi in the corner. Purex Triton FNS Plus 48 DE filter. Taylor (high) test kit.
    Centurion pump model# 7-168887-06. Built 2001 and filled from a well since then.

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    mikemass's Avatar
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    Re: Holding FC better than I expected

    I love an outside the box thinker. I wonder if that works. If not, it would be good to know if there is a way to trick the test into reading a higher Cl level on a DPD test. I know you can't get the ultra high readings. But if you are running a little over the max of 5.0 on a DPD test and that's all we have, it would be helpful.
    25 + year pool owner. Current pool (going on 11th year) - 38K gallon in ground Gunite/White Plaster, Spillover Spa, Hayward Cartridge Filter, Hayward 450k BTU NG Heater, Hayward Goldline Aqua Logic control with T-Cell-15 Salt Water Cell, Dolphin Explorer.
    You Need: Bleach, a A Test Kit & a Bookmark to "Pool School". Now what's your question?

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    Richard320's Avatar
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    Re: Holding FC better than I expected

    I should interject her to mention that at really high FC levels, the DPD reagent bleaches out.

    The OTO (yellow) FC test goes through different shades from pale yellow to blinding tweety bird yellow to school bus (Or Caterpillar equipment) yellow to hunter orange to pumpkin orange and into shades of brown. But none of them are really accurate.

    The FAS-DPD powder and drops will measure up to 50 FC with as much as .2 resolution. If you have the patience for that many drops. You can buy just the FAS-DPD add-on here
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