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Thread: When to test FC after soak?

  1. Back To Top    #1

    Join Date
    Jun 2008

    When to test FC after soak?

    Hi. I just switched over my hot-tub to the BBB method. I'm trying to figure out what my dosage needs to be after a soak.

    How long after I get out should I test for FC and adjust as necessary? Right after I get out, 15 mins later, the following morning, etc?

    Also, when I add bleach, should I turn my pumps on and let them run (15 min cycle), or can I shut them off after 5 mins or so, or will my 24 hr continuous pump be enough to circulate the bleach? If I use the 24 hr pump, I'm alittle worried about the water that's in the pumps and the associated plumbing not getting sanitized. But the hot-tub cycles twice a day for a few minutes.

    Thanks for the advice and help,

    Doughboy 16' x 24' AGP, 9200g, Hayward 1 1/2 HP pump and Sand Filter. Sparkling water due to BBB method.
    Leisure Time Spa, Salida G-3, 275g. Also clear and clean due to BBB.

  2. Back To Top    #2

    Join Date
    Mar 2007
    San Rafael, CA USA

    Re: When to test FC after soak?


    If you had any Free Chlorine (FC) level when you got into the tub and then tested the water soon after you got out, you would likely end up measuring Combined Chlorine (CC) from the ammonia in sweat that still needed to get broken down. I think the best thing to do is to measure the FC level just before you get in. If it's very close to zero, then you aren't adding enough chlorine. As for what level it should be when you get in, that depends on your philosophy.

    For the best sanitation, you would have the FC be high enough to handle your soaking, probably on the order of 4 ppm or so. However, this can lead to smelling chlorine (actually monochloramine or combined chlorine from your sweat) during the soak. Since soaking isn't very long and since you generally aren't worried about person-to-person transmission of pathogens in a private spa, some people soak with a low FC level (around 1 ppm) and then add the chlorine right after they soak. There's more risk of having some hot tub bacteria form biofilms on surfaces while you soak but in practice I haven't seen that be a problem reported on forums (usually, the more common, though still infrequent, problem is continued use of Dichlor and having hot tub itch/rash after more than a month of such use).

    I assume that you start out using Dichlor to cumulatively get to around 20 ppm CYA (usually takes about a week of daily dosing) and then switched to bleach. You want to have some CYA in the water, but not too much.

    The normal circulation should be fine for mixing the chlorine and I think the twice a day hot tub cycling is OK for the pipes. Obviously, more continuous flow through such pipes would be better, but the electricity cost, aeration, and resulting pH rise would be excessive.

    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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