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Thread: Fresh Fill - Now What

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    Fresh Fill - Now What

    Jacuzzi 375 gallon with ClearRay. I did not sanitize all last year...just the ClearRay bulb per Jacuzzi. I think this was wrong...luckily never had a problem with itch etc...

    Just emptied, and filled with tap water....now realize I could have used pool water. Next time...

    96 degrees (still warming up from fill)

    0 FC
    8.2+ pH
    60 TA
    150 CH
    0 CYA

    How much dichlor (Chlor-Brite) should I add to bring up FC & CYA? and should I add muratic acid now to bring down pH, if so, how much? I don't quite understand the pool calculator for the 1st fill and dichlor use.

    Thanks.
    Fiberglass Caged Pool Circa 1995
    15' x 32' - 16k Gallons
    Central, FL
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    Mod Squad woodyp's Avatar
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    Re: Fresh Fill - Now What

    Just put in your number of gallons (which you know) at the top of the pool math calculator. Put in your NOW numbers in the first block in each category--then your TARGET (wanna be) number in the block to the right. Hit calculate and dose accordingly. Now is as good a time to learn as any.
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    bridgman's Avatar
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    Re: Fresh Fill - Now What

    If you're using dichlor then bleach the CYA won't come up immediately, so focus on getting the right FC level and keep track of the amount of dichlor you add, then switch to bleach when you've added that amount.

    30 ppm of CYA is a good number, and also happens to be the lowest level my test kit can reliably read. I ran with 20 ppm CYA until I got a good test kit, then I raised it to 30 so the test kit could measure it. There's probably something fundamentally wrong with that but I can live with it

    There's an "Effects of adding chemicals" section near the bottom you can use to figure out the total amount of dichlor required to reach your target CYA level, although you have to do it via the "trial and error" approach (hint - try 3 oz of dichlor). For my tub (which is larger than yours) a *total* of 6 oz of dichlor is enough to take CYA just past 30 ppm, so I dose with dichlor according to what PoolMath tells me until I get to a total of 6 oz, then switch to dosing with bleach.

    Note that the target FC range per PoolMath is 1-3 ppm when you have 0 CYA (fresh fill) and 2-6 ppm when you have 30 ppm CYA (where I switch to bleach). In a perfect world you would ramp up your target FC as you get closer to the target CYA level, but you could probably keep your target at 3 until you reach 30ppm CYA and then set your target to 6. By target I mean the FC level you dose up to, with the idea being that it will be lower but still in range when you test the next day.

    I have only run through the exercise once (twice if you count discovering the dichlor/bleach method after running the tub on dichlor-only for a while) -- the water has been so nice and clean I haven't bothered changing it for a few months now.
    Cedar hot tub, 680 US gallons - Snorkel wood-burning heater, canoe paddle, "offline" Intex 1000 GPH pump/filter with skimmer

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    Isaac-1's Avatar
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    Re: Fresh Fill - Now What

    Also note dichlor is acidic so will lower your pH some
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    Re: Fresh Fill - Now What

    Thanks all....Bridgman had the main info I was looking for...basically dose for target FC.....with dichlor until CYA gets to right level...then switch to bleach... my brain was trying to dose for CYA at same time as FC
    Fiberglass Caged Pool Circa 1995
    15' x 32' - 16k Gallons
    Central, FL
    Hayward Cartridge Filter System

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    bridgman's Avatar
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    Re: Fresh Fill - Now What

    Yeah, chem geek and others had absolutely brilliant posts on this back in 2007 or so... they deserve to be stickied somewhere unless they have been replaced by a newer and better regimen.
    Cedar hot tub, 680 US gallons - Snorkel wood-burning heater, canoe paddle, "offline" Intex 1000 GPH pump/filter with skimmer

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    Re: Fresh Fill - Now What

    There is Using Chlorine in a Spa that was written by Nitro based on what I came up with for the Dichlor-then-bleach method.
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    bridgman's Avatar
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    Re: Fresh Fill - Now What

    You mean the sticky'd thread that I've been skipping over every day ? D'oh !!

    (and thanks !!)

    IMO your comment in post #6 of that thread deserves a bit more visbility :

    Also, the 7 ppm FC in 350 gallons per person per hour of soaking guideline (at 104F) isn't in the Pool School either. This translates into amounts that are independent of spa volume of 3-1/2 teaspoons of Dichlor or 5 fluid ounces of 6% bleach or 7 teaspoons of MPS non-chlorine shock. These are conservative amounts of chlorine needed to oxidize bather waste (mostly ammonia/urea from sweat/urine). The biggest mistake most spa users make is not using enough oxidizer in their spas, especially if such spas are more heavily used.
    I found the idea of adding a certain number of ppm FC to deal with bather load baffling (it seemed intuitively wrong), but once I read one of your posts mentioning that the post-use dose for dealing with bather load should be an absolute amount everything clicked in my head.
    Cedar hot tub, 680 US gallons - Snorkel wood-burning heater, canoe paddle, "offline" Intex 1000 GPH pump/filter with skimmer

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    Re: Fresh Fill - Now What

    Yeah, that 7 ppm FC is PER 350 GALLONS. It would only be 3.5 ppm FC in 700 gallons. The amount of chlorine is absolute per person-hour of soaking. The FC level corresponding to that will vary depending on the spa size. The typical spa store recommendations of adding some fixed amount after a soak are on the right track and they usually say it's an amount per person, but they don't usually say anything about it also being proportional to how long you soak.

    Then there are subtleties such as water temperature (one sweats more at higher temperature) and whether one has an ozonator. Ozone oxidizes both bather waste as well as chlorine so in high bather-load situations ozone reduces the amount of chlorine you need but in low bather-load situations (i.e. days of no use in between soaks) it increases the amount of (background dose) chlorine you need.
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