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Thread: Pool and attached spa, looking for water chemistry advice

  1. #1
    Join Date
    Sep 2014
    Location
    Tucson, AZ
    Posts
    254

    Question Pool and attached spa, looking for water chemistry advice

    Just to start off on the right foot - I know the Pool Forum is mainly about pools and I know that pool water chemistry and spa water chemistry are different beasts. That being said, I'm sure there's a subset of PF'ers that, like me, have pools with attached spas. So if this thread is not in the right Forum, feel free to move it.

    -----------------------------------------

    So our pool has an attached spa that we like to use on occasions. The way our plumbing and automation works (and I think this is fairly standard) is that we have three returns to the pool and one return to the spa (aside from the five spa jets that only operate when the plumbing is in spa mode). I can split the return water between the pool returns and spa returns and typically leave it at 50/50 so that the spillway water feature runs. I plan to automate that three-way valve someday soon so I can better control my water feature.

    All the above means is that the pool water and spa water start off with the same chemical balance. I typically try to achieve the following chemical ranges and I'm almost always in these ranges -

    FC 5-7ppm
    pH 7.6-7.8
    CYA 50-70ppm (current value is 70ppm)
    TA 70-90ppm
    CH - 550ppm (current value)
    Salt - ~4000ppm (current value)
    Borates ~ 50ppm (current value)

    The spa is 650 gallons and when I run it, I typically find 95F to be a very comfortable temperature. The IntelliFlo is set to it's highest speed and there is no booster pump, just a Venturi air draw to make the bubbles. The IntelliChlor auto-magically switches over to Spa-mode output which is around 2% power (max is 5% in spa mode).

    So here are the questions -

    1. What would be optimal spa water pH and TA to achieve prior to getting in the spa?

    2. Is it better to bump up the FC prior to going in or afterwards?

    3. Is there anything else I'm missing?

    In the past, I would just run the spa with the water balance as-is and then return the system to pool mode and let all the spa water spill over into the pool. I know from measuring the spa water after use that the pH is typically quite high and the CC's are up from the bather load (I think I can actually smell the chloramines) and I imagine the TA is probably quite low from CO2 outgassing. The spa volume is only a small fraction of the pool volume (16,000 gallons) but I don't like dumping waste water into my typically sparkly pool.

    Any advice or pointers others might have would be most appreciated.

    Thanks.
    16k gal IG gunite PebbleTec (Caribbean Blue), 18' x 36' free form with raised spa/spillway and separate rock waterfall. All Pentair Equipment pad - 3HP IntelliFlo VS / 1.5HP WhisperFlo, MasterTemp 400k BTU/hr heater, QuadDE-100 filter, IC40 SWCG, IntelliTouch/EasyTouch Controls

  2. #2
    Join Date
    Jul 2010
    Location
    Largo, Florida
    Posts
    529

    Default Re: Pool and attached spa, looking for water chemistry advice

    I have a nearly identical setup. I run my spa at 101, and I do turn my swcg OFF during spa operation. If I don't turn it off first, I get that strong chlorine smell when soaking. Try giving that a shot maybe?

    After I'm done, I set it back to 50/50 and let the water mix. The next day I test and adjust the pool water chemistry as I normally would.

    The pH and TA may be off in the spa water but it's been through the filter a lot more than the rest of the pool water. I consider it a wash.
    rectangle 11.5K gal IG concrete pool;; 125sf cartridge filter; 2hp 1 speed pump; K-2006, k-1766; PF:10

  3. #3
    Join Date
    Sep 2014
    Location
    Tucson, AZ
    Posts
    254

    Default Re: Pool and attached spa, looking for water chemistry advice

    Quote Originally Posted by kelemvor View Post
    I have a nearly identical setup. I run my spa at 101, and I do turn my swcg OFF during spa operation. If I don't turn it off first, I get that strong chlorine smell when soaking. Try giving that a shot maybe?

    After I'm done, I set it back to 50/50 and let the water mix. The next day I test and adjust the pool water chemistry as I normally would.

    The pH and TA may be off in the spa water but it's been through the filter a lot more than the rest of the pool water. I consider it a wash.
    Thanks. agree that running the IC40 is probably not a good idea. Even my PB told me that the spa can get overly chlorinated with long run times since it's such a small volume of water. I may just bump up the FC prior to use and then shutoff the IC.

    One of my many to-do's is to run the spa without heat to see how quickly I can drop the TA using the acid-aeration method. I'd like to lower the TA and get the pH down a bit prior to using it as I don't want my high CH water to scale.
    16k gal IG gunite PebbleTec (Caribbean Blue), 18' x 36' free form with raised spa/spillway and separate rock waterfall. All Pentair Equipment pad - 3HP IntelliFlo VS / 1.5HP WhisperFlo, MasterTemp 400k BTU/hr heater, QuadDE-100 filter, IC40 SWCG, IntelliTouch/EasyTouch Controls

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