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Thread: Balancing after Reverse Osmosis R/O filtration?

  1. Back To Top    #1

    Join Date
    Apr 2017

    Balancing after Reverse Osmosis R/O filtration?

    Good morning y'all! Newbie here in the Dallas TX area!
    We just got our pool filtered two days ago! And I'd appreciate some advice on the balancing! We decided to filter instead of drain-refill because I really wanted to try to conserve water as much as possible, and I believe we needed to filter because of high CYA and high CH. (all test done with Taylor K2006 kit)
    Here below the values pre- and post- filtration. Water was (and still is) crystal clear, but we have some greenish stains on the walls I'm convinced is the beginning of some algae...hopefully with the lower CYA levels I'll be able to clear them out more easily.
    Pre R/O Post R/O
    FC 14.5 2
    CC 0 0
    pH 7.8 7.4
    TA 120 40
    CH 500 120
    CYA 120 <30
    Temp 70F 70F
    SI ---- -0.8

    It took only 12 hours and it was done. Yesterday, we put in a floater with 4x3" trichlor-pucks to start adding some chlorine and CYA (slowly for a total ~6.4 ppm). Then Last night I decided to bump up the TA from 40 ppm to 80 ppm, to have a better buffer for the pH. I also wanted to raise FC to 5 ppm (it had dropped only down to 1.5 ppm). I had some Ca-hypo (65%) so decided to use it, since also I wanted to raise the CH a bit.
    I used the pol math calculator, and put in 12 Lb baking soda and 500 g (1.1 Lb) of Ca-Hypo, and let the pump run for 3 hours afterwards to mix.
    This morning:
    FC = 5.4
    pH = 7.8
    Am I missing something here? I was not expecting the pH to go up that much.... Did I tinker with too many parameters at once??
    What do you recommend next? Should I try to lower the pH (it took 2 drops of "acid demand" to bring it back to 7.4)? Should I remeasure TA and wait to see where the pH goes? If I got the chemistry right, the Ca-Hypo (or Na-hypochlorite) are basic reactions, but once the HClO is used up it's the pH spike is transient?
    I eventually would like to follow BBB method, and use the pucks only when/if traveling.
    Thanks in advance! I've been reading on the forum for a while and found it REALLY helpful, but I'm kind of stuck now

    PS: thanks also to chem geek for the in-depth posts in the "deep end" got me to open my chemistry books once again!!
    ~21-25,000 gal, Inground gunite, Pentair DE filter, Pentair pump (one speed), Taylor K2006 (FAS-DPD) test kit

  2. Back To Top    #2
    Richard320's Avatar
    Join Date
    Jan 2010
    San Dimas, CA (LA County)

    Re: Balancing after Reverse Osmosis R/O filtration?

    At the instant you added the baking soda, the pH would have stayed the same. But the water was moving and aerating and the higher TA just nudged the pH up a little. I wouldn't be alarmed. pH might just sit there for weeks or it may need a touch of acid tomorrow to bring it down again. You'll just have to keep track of things until you find the sweet spot for your pool.
    16K freeform gunite with spa; Pentair 4000 DE filter; Century Whisperflow 1 HP; Pentair Minimax heater.
    Troublefree does not mean Maintenancefree. It's like brushing your teeth: You can spend a couple minutes a day and pennies a week or go to the dentist once a year and spend several thousand dollars.
    A pool is like a pet - you have to feed it every day, even the days you don't want to play with it!

  3. Back To Top    #3

    Join Date
    Apr 2017

    Re: Balancing after Reverse Osmosis R/O filtration?

    If I were you, I would remove the word "eventually" in your statement "eventually follow the BBB method."

    In any event, I would remove the pucks and the cal hypo. Save the pucks for travel or when you modestly need to add some CYA, but don't waste time using them to raise your CYA now. It will take too long, and you should really get your CYA to 30-40 now. Go buy some stabilizer and using the pool calculator put it next to the return jet and let it absorb into the water. Get your FC level up to proper levels. Monitor your PH for a few days, and if it starts creeping to 8.0 then add needed muriatic acid to get it back to 7.4-7.8.

    If you need calcium, I would also add that separately instead of relying on the cal hypo.
    16,000 gallon in-ground pebble tec pool. Hayward SP3400VSP Eco-Star Pump, Pentair Triton 2 TR-100 sand filter, A&A 5-port in-floor pool cleaner, Pentair Intellibrite 5g color changing pool light, Polaris 965iQ Robotic Pool Cleaner, OG Pool Math Subscriber and most importantly a Taylor K-2006C test kit.
    Test Kits Compared
    | SLAM | Chlorine / CYA Chart |

  4. Back To Top    #4

    Join Date
    Apr 2017

    Post Re: Balancing after Reverse Osmosis R/O filtration?

    Thanks for the input! I'll see where my numbers are tonight and how much FC I's a bright sunny day today!!
    I think my CYA is close to 30 ppm (the dot is very cloudy at the 30 mark, but still visible).

    To SpinHD: I was just finishing up some of the supplies the previous owner had, that's why I said "eventually". I do very much prefer the idea of adding one chemical at a time, since it gives you a much better control!

    btw the funny story about this pool is that the previous owner had pucks EVERYWHERE: in the 2 skimmers (3-4 pucks each) and in a floater (another 4), and he told me "oh, just keep adding the pucks and you'll be fine!" turns out he was quite lucky, because there was a sizable leak at the pump and he might have gotten to a steady state (or very low rising CYA) with all the water loss and back-flushing. We repaired the leak in January and in March I started having problems (yes, I did not cleanup the leaves right away after a storm too...) with some "green stuff" on the walls! That's when I really started to read about the chemistry involved, and found this forum! So the pucks went out, started adding bleach (FC kept at ~15 ppm) and scheduled the R/O filtration!!
    ~21-25,000 gal, Inground gunite, Pentair DE filter, Pentair pump (one speed), Taylor K2006 (FAS-DPD) test kit

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